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Hazen-Williams Equation

Fluid Mechanics · FE Reference Handbook section

Fluid Mechanics
4 formulas
10 exam-style examples
~53 min
All Fluid Mechanics lectures

Core formulas for this FE topic

Definitions, applicability, units, assumptions and worked examples for each relation.

Worked exam-style examples

The four ways this section is written on the real exam — thoughts first, then equations, then substitution.

Example 1
Hazen-Williams equation — solve for velocity — Hazen-Williams Equation

the Hazen-Williams equation for a water distribution pipeline Given Hazen-Williams coefficient (C_HW) = 116.0; hydraulic radius (R_H) = 0.2100 m; slope of energy grade line (S) = 0.0161 m/m, determine the velocity (V) in m/s.

Given

  • Hazen−Williamscoefficient(CHW)=116.0Hazen-Williams coefficient (C_HW) = 116.0
  • hydraulicradius(RH)=0.2100mhydraulic radius (R_H) = 0.2100 m
  • slopeofenergygradeline(S)=0.0161m/mslope of energy grade line (S) = 0.0161 m/m

Find

velocity (V), in m/s

Start with the thinking

  • The governing relation printed in this handbook section is Hazen-Williams equation.
  • Everything except V is given, so isolate V symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The Hazen-Williams equation estimates flow velocity in a pipeline given its roughness coefficient and slope.
D₁=150D₂=150VS

Figure 1 — schematic for Hazen-Williams equation — solve for velocity — Hazen-Williams Equation

Step-by-step solution

  1. Step 1 — State the governing relation:

    V=0.849 CHWRH0.63S0.54V = 0.849\, C_{HW} R_H^{0.63} S^{0.54}
  2. Step 2 — Rearrange the relation so that V stands alone on the left-hand side.

  3. Step 3 — List the givens: Hazen-Williams coefficient (C_HW) = 116.0, hydraulic radius (R_H) = 0.2100 m, slope of energy grade line (S) = 0.0161 m/m.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    V=3.9632 m/sV = 3.9632\ \text{m/s}
  6. Step 6 — Check: returning V = 3.9632 m/s to

    V=0.849 CHWRH0.63S0.54V = 0.849\, C_{HW} R_H^{0.63} S^{0.54}

    reproduces the given quantities, and both sides carry the same units.

Answer:
V=3.9632 m/sV = 3.9632\ \text{m/s}

Why the other options are there

  • 7.9265 — kept a factor of two that cancels in the correct rearrangement.
  • 1.9816 — dropped that same factor in the other direction.
  • 4.3596 — rounded an intermediate value before the final step.

Reference: FE Handbook — Hazen-Williams Equation

Example 2
Hazen-Williams equation — solve for Hazen-Williams coefficient — Hazen-Williams Equation (2)

the Hazen-Williams equation applied to a ductile-iron pipe Given hydraulic radius (R_H) = 0.1800 m; slope of energy grade line (S) = 0.0153 m/m; velocity (V) = 2.4000 m/s, determine the Hazen-Williams coefficient (C_HW).

Given

  • hydraulicradius(RH)=0.1800mhydraulic radius (R_H) = 0.1800 m
  • slopeofenergygradeline(S)=0.0153m/mslope of energy grade line (S) = 0.0153 m/m
  • velocity(V)=2.4000m/svelocity (V) = 2.4000 m/s

Find

Hazen-Williams coefficient (C_HW)

Start with the thinking

  • The governing relation printed in this handbook section is Hazen-Williams equation.
  • Everything except C_HW is given, so isolate C_HW symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The Hazen-Williams equation estimates flow velocity in a pipeline given its roughness coefficient and slope.
D₁=150D₂=150VS

Figure 2 — schematic for Hazen-Williams equation — solve for Hazen-Williams coefficient — Hazen-Williams Equation (2)

Step-by-step solution

  1. Step 1 — State the governing relation:

    V=0.849 CHWRH0.63S0.54V = 0.849\, C_{HW} R_H^{0.63} S^{0.54}
  2. Step 2 — Rearrange the relation so that C_HW stands alone on the left-hand side.

  3. Step 3 — List the givens: hydraulic radius (R_H) = 0.1800 m, slope of energy grade line (S) = 0.0153 m/m, velocity (V) = 2.4000 m/s.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    CHW=79.5698C_{HW} = 79.5698
  6. Step 6 — Check: returning C_HW = 79.5698 to

    V=0.849 CHWRH0.63S0.54V = 0.849\, C_{HW} R_H^{0.63} S^{0.54}

    reproduces the given quantities, and both sides carry the same units.

Answer:
CHW=79.5698C_{HW} = 79.5698

Why the other options are there

  • 159.1 — kept a factor of two that cancels in the correct rearrangement.
  • 39.7849 — dropped that same factor in the other direction.
  • 87.5268 — rounded an intermediate value before the final step.

Reference: FE Handbook — Hazen-Williams Equation

Example 3
Hazen-Williams equation — solve for velocity (case 2) — Hazen-Williams Equation (3)

the Hazen-Williams equation to size a municipal pipe Given Hazen-Williams coefficient (C_HW) = 97.0000; hydraulic radius (R_H) = 0.2500 m; slope of energy grade line (S) = 0.0197 m/m, determine the velocity (V) in m/s.

Given

  • Hazen−Williamscoefficient(CHW)=97.0000Hazen-Williams coefficient (C_HW) = 97.0000
  • hydraulicradius(RH)=0.2500mhydraulic radius (R_H) = 0.2500 m
  • slopeofenergygradeline(S)=0.0197m/mslope of energy grade line (S) = 0.0197 m/m

Find

velocity (V), in m/s

Start with the thinking

  • The governing relation printed in this handbook section is Hazen-Williams equation.
  • Everything except V is given, so isolate V symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The Hazen-Williams equation estimates flow velocity in a pipeline given its roughness coefficient and slope.
D₁=150D₂=150VS

Figure 3 — schematic for Hazen-Williams equation — solve for velocity (case 2) — Hazen-Williams Equation (3)

Step-by-step solution

  1. Step 1 — State the governing relation:

    V=0.849 CHWRH0.63S0.54V = 0.849\, C_{HW} R_H^{0.63} S^{0.54}
  2. Step 2 — Rearrange the relation so that V stands alone on the left-hand side.

  3. Step 3 — List the givens: Hazen-Williams coefficient (C_HW) = 97.0000, hydraulic radius (R_H) = 0.2500 m, slope of energy grade line (S) = 0.0197 m/m.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    V=4.1247 m/sV = 4.1247\ \text{m/s}
  6. Step 6 — Check: returning V = 4.1247 m/s to

    V=0.849 CHWRH0.63S0.54V = 0.849\, C_{HW} R_H^{0.63} S^{0.54}

    reproduces the given quantities, and both sides carry the same units.

Answer:
V=4.1247 m/sV = 4.1247\ \text{m/s}

Why the other options are there

  • 8.2494 — kept a factor of two that cancels in the correct rearrangement.
  • 2.0624 — dropped that same factor in the other direction.
  • 4.5372 — rounded an intermediate value before the final step.

Reference: FE Handbook — Hazen-Williams Equation

Example 4
Hazen-Williams equation — solve for Hazen-Williams coefficient (case 2) — Hazen-Williams Equation (4)

the Hazen-Williams equation for a water distribution pipeline Given hydraulic radius (R_H) = 0.0300 m; slope of energy grade line (S) = 0.0181 m/m; velocity (V) = 0.8000 m/s, determine the Hazen-Williams coefficient (C_HW).

Given

  • hydraulicradius(RH)=0.0300mhydraulic radius (R_H) = 0.0300 m
  • slopeofenergygradeline(S)=0.0181m/mslope of energy grade line (S) = 0.0181 m/m
  • velocity(V)=0.8000m/svelocity (V) = 0.8000 m/s

Find

Hazen-Williams coefficient (C_HW)

Start with the thinking

  • The governing relation printed in this handbook section is Hazen-Williams equation.
  • Everything except C_HW is given, so isolate C_HW symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The Hazen-Williams equation estimates flow velocity in a pipeline given its roughness coefficient and slope.
D₁=150D₂=150VS

Figure 4 — schematic for Hazen-Williams equation — solve for Hazen-Williams coefficient (case 2) — Hazen-Williams Equation (4)

Step-by-step solution

  1. Step 1 — State the governing relation:

    V=0.849 CHWRH0.63S0.54V = 0.849\, C_{HW} R_H^{0.63} S^{0.54}
  2. Step 2 — Rearrange the relation so that C_HW stands alone on the left-hand side.

  3. Step 3 — List the givens: hydraulic radius (R_H) = 0.0300 m, slope of energy grade line (S) = 0.0181 m/m, velocity (V) = 0.8000 m/s.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    CHW=74.8944C_{HW} = 74.8944
  6. Step 6 — Check: returning C_HW = 74.8944 to

    V=0.849 CHWRH0.63S0.54V = 0.849\, C_{HW} R_H^{0.63} S^{0.54}

    reproduces the given quantities, and both sides carry the same units.

Answer:
CHW=74.8944C_{HW} = 74.8944

Why the other options are there

  • 149.8 — kept a factor of two that cancels in the correct rearrangement.
  • 37.4472 — dropped that same factor in the other direction.
  • 82.3839 — rounded an intermediate value before the final step.

Reference: FE Handbook — Hazen-Williams Equation

Example 5
Hazen-Williams equation — solve for velocity (case 3) — Hazen-Williams Equation (5)

the Hazen-Williams equation applied to a ductile-iron pipe Given Hazen-Williams coefficient (C_HW) = 139.0; hydraulic radius (R_H) = 0.1200 m; slope of energy grade line (S) = 0.0021 m/m, determine the velocity (V) in m/s.

Given

  • Hazen−Williamscoefficient(CHW)=139.0Hazen-Williams coefficient (C_HW) = 139.0
  • hydraulicradius(RH)=0.1200mhydraulic radius (R_H) = 0.1200 m
  • slopeofenergygradeline(S)=0.0021m/mslope of energy grade line (S) = 0.0021 m/m

Find

velocity (V), in m/s

Start with the thinking

  • The governing relation printed in this handbook section is Hazen-Williams equation.
  • Everything except V is given, so isolate V symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The Hazen-Williams equation estimates flow velocity in a pipeline given its roughness coefficient and slope.
D₁=150D₂=150VS

Figure 5 — schematic for Hazen-Williams equation — solve for velocity (case 3) — Hazen-Williams Equation (5)

Step-by-step solution

  1. Step 1 — State the governing relation:

    V=0.849 CHWRH0.63S0.54V = 0.849\, C_{HW} R_H^{0.63} S^{0.54}
  2. Step 2 — Rearrange the relation so that V stands alone on the left-hand side.

  3. Step 3 — List the givens: Hazen-Williams coefficient (C_HW) = 139.0, hydraulic radius (R_H) = 0.1200 m, slope of energy grade line (S) = 0.0021 m/m.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    V=1.1112 m/sV = 1.1112\ \text{m/s}
  6. Step 6 — Check: returning V = 1.1112 m/s to

    V=0.849 CHWRH0.63S0.54V = 0.849\, C_{HW} R_H^{0.63} S^{0.54}

    reproduces the given quantities, and both sides carry the same units.

Answer:
V=1.1112 m/sV = 1.1112\ \text{m/s}

Why the other options are there

  • 2.2225 — kept a factor of two that cancels in the correct rearrangement.
  • 0.5556 — dropped that same factor in the other direction.
  • 1.2224 — rounded an intermediate value before the final step.

Reference: FE Handbook — Hazen-Williams Equation

Example 6
Hazen-Williams equation — solve for Hazen-Williams coefficient (case 3) — Hazen-Williams Equation (6)

the Hazen-Williams equation to size a municipal pipe Given hydraulic radius (R_H) = 0.1900 m; slope of energy grade line (S) = 0.0113 m/m; velocity (V) = 0.5500 m/s, determine the Hazen-Williams coefficient (C_HW).

Given

  • hydraulicradius(RH)=0.1900mhydraulic radius (R_H) = 0.1900 m
  • slopeofenergygradeline(S)=0.0113m/mslope of energy grade line (S) = 0.0113 m/m
  • velocity(V)=0.5500m/svelocity (V) = 0.5500 m/s

Find

Hazen-Williams coefficient (C_HW)

Start with the thinking

  • The governing relation printed in this handbook section is Hazen-Williams equation.
  • Everything except C_HW is given, so isolate C_HW symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The Hazen-Williams equation estimates flow velocity in a pipeline given its roughness coefficient and slope.
D₁=150D₂=150VS

Figure 6 — schematic for Hazen-Williams equation — solve for Hazen-Williams coefficient (case 3) — Hazen-Williams Equation (6)

Step-by-step solution

  1. Step 1 — State the governing relation:

    V=0.849 CHWRH0.63S0.54V = 0.849\, C_{HW} R_H^{0.63} S^{0.54}
  2. Step 2 — Rearrange the relation so that C_HW stands alone on the left-hand side.

  3. Step 3 — List the givens: hydraulic radius (R_H) = 0.1900 m, slope of energy grade line (S) = 0.0113 m/m, velocity (V) = 0.5500 m/s.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    CHW=20.7576C_{HW} = 20.7576
  6. Step 6 — Check: returning C_HW = 20.7576 to

    V=0.849 CHWRH0.63S0.54V = 0.849\, C_{HW} R_H^{0.63} S^{0.54}

    reproduces the given quantities, and both sides carry the same units.

Answer:
CHW=20.7576C_{HW} = 20.7576

Why the other options are there

  • 41.5153 — kept a factor of two that cancels in the correct rearrangement.
  • 10.3788 — dropped that same factor in the other direction.
  • 22.8334 — rounded an intermediate value before the final step.

Reference: FE Handbook — Hazen-Williams Equation

Example 7
Hazen-Williams equation — solve for velocity (case 4) — Hazen-Williams Equation (7)

the Hazen-Williams equation for a water distribution pipeline Given Hazen-Williams coefficient (C_HW) = 126.0; hydraulic radius (R_H) = 0.1800 m; slope of energy grade line (S) = 0.0112 m/m, determine the velocity (V) in m/s.

Given

  • Hazen−Williamscoefficient(CHW)=126.0Hazen-Williams coefficient (C_HW) = 126.0
  • hydraulicradius(RH)=0.1800mhydraulic radius (R_H) = 0.1800 m
  • slopeofenergygradeline(S)=0.0112m/mslope of energy grade line (S) = 0.0112 m/m

Find

velocity (V), in m/s

Start with the thinking

  • The governing relation printed in this handbook section is Hazen-Williams equation.
  • Everything except V is given, so isolate V symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The Hazen-Williams equation estimates flow velocity in a pipeline given its roughness coefficient and slope.
D₁=150D₂=150VS

Figure 7 — schematic for Hazen-Williams equation — solve for velocity (case 4) — Hazen-Williams Equation (7)

Step-by-step solution

  1. Step 1 — State the governing relation:

    V=0.849 CHWRH0.63S0.54V = 0.849\, C_{HW} R_H^{0.63} S^{0.54}
  2. Step 2 — Rearrange the relation so that V stands alone on the left-hand side.

  3. Step 3 — List the givens: Hazen-Williams coefficient (C_HW) = 126.0, hydraulic radius (R_H) = 0.1800 m, slope of energy grade line (S) = 0.0112 m/m.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    V=3.2113 m/sV = 3.2113\ \text{m/s}
  6. Step 6 — Check: returning V = 3.2113 m/s to

    V=0.849 CHWRH0.63S0.54V = 0.849\, C_{HW} R_H^{0.63} S^{0.54}

    reproduces the given quantities, and both sides carry the same units.

Answer:
V=3.2113 m/sV = 3.2113\ \text{m/s}

Why the other options are there

  • 6.4226 — kept a factor of two that cancels in the correct rearrangement.
  • 1.6056 — dropped that same factor in the other direction.
  • 3.5324 — rounded an intermediate value before the final step.

Reference: FE Handbook — Hazen-Williams Equation

Example 8
Hazen-Williams equation — solve for Hazen-Williams coefficient (case 4) — Hazen-Williams Equation (8)

the Hazen-Williams equation applied to a ductile-iron pipe Given hydraulic radius (R_H) = 0.2900 m; slope of energy grade line (S) = 0.0098 m/m; velocity (V) = 1.3500 m/s, determine the Hazen-Williams coefficient (C_HW).

Given

  • hydraulicradius(RH)=0.2900mhydraulic radius (R_H) = 0.2900 m
  • slopeofenergygradeline(S)=0.0098m/mslope of energy grade line (S) = 0.0098 m/m
  • velocity(V)=1.3500m/svelocity (V) = 1.3500 m/s

Find

Hazen-Williams coefficient (C_HW)

Start with the thinking

  • The governing relation printed in this handbook section is Hazen-Williams equation.
  • Everything except C_HW is given, so isolate C_HW symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The Hazen-Williams equation estimates flow velocity in a pipeline given its roughness coefficient and slope.
D₁=150D₂=150VS

Figure 8 — schematic for Hazen-Williams equation — solve for Hazen-Williams coefficient (case 4) — Hazen-Williams Equation (8)

Step-by-step solution

  1. Step 1 — State the governing relation:

    V=0.849 CHWRH0.63S0.54V = 0.849\, C_{HW} R_H^{0.63} S^{0.54}
  2. Step 2 — Rearrange the relation so that C_HW stands alone on the left-hand side.

  3. Step 3 — List the givens: hydraulic radius (R_H) = 0.2900 m, slope of energy grade line (S) = 0.0098 m/m, velocity (V) = 1.3500 m/s.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    CHW=42.1554C_{HW} = 42.1554
  6. Step 6 — Check: returning C_HW = 42.1554 to

    V=0.849 CHWRH0.63S0.54V = 0.849\, C_{HW} R_H^{0.63} S^{0.54}

    reproduces the given quantities, and both sides carry the same units.

Answer:
CHW=42.1554C_{HW} = 42.1554

Why the other options are there

  • 84.3108 — kept a factor of two that cancels in the correct rearrangement.
  • 21.0777 — dropped that same factor in the other direction.
  • 46.3709 — rounded an intermediate value before the final step.

Reference: FE Handbook — Hazen-Williams Equation

Example 9
Hazen-Williams equation — solve for velocity (case 5) — Hazen-Williams Equation (9)

the Hazen-Williams equation to size a municipal pipe Given Hazen-Williams coefficient (C_HW) = 116.0; hydraulic radius (R_H) = 0.0300 m; slope of energy grade line (S) = 0.0122 m/m, determine the velocity (V) in m/s.

Given

  • Hazen−Williamscoefficient(CHW)=116.0Hazen-Williams coefficient (C_HW) = 116.0
  • hydraulicradius(RH)=0.0300mhydraulic radius (R_H) = 0.0300 m
  • slopeofenergygradeline(S)=0.0122m/mslope of energy grade line (S) = 0.0122 m/m

Find

velocity (V), in m/s

Start with the thinking

  • The governing relation printed in this handbook section is Hazen-Williams equation.
  • Everything except V is given, so isolate V symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The Hazen-Williams equation estimates flow velocity in a pipeline given its roughness coefficient and slope.
D₁=150D₂=150VS

Figure 9 — schematic for Hazen-Williams equation — solve for velocity (case 5) — Hazen-Williams Equation (9)

Step-by-step solution

  1. Step 1 — State the governing relation:

    V=0.849 CHWRH0.63S0.54V = 0.849\, C_{HW} R_H^{0.63} S^{0.54}
  2. Step 2 — Rearrange the relation so that V stands alone on the left-hand side.

  3. Step 3 — List the givens: Hazen-Williams coefficient (C_HW) = 116.0, hydraulic radius (R_H) = 0.0300 m, slope of energy grade line (S) = 0.0122 m/m.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    V=1.0014 m/sV = 1.0014\ \text{m/s}
  6. Step 6 — Check: returning V = 1.0014 m/s to

    V=0.849 CHWRH0.63S0.54V = 0.849\, C_{HW} R_H^{0.63} S^{0.54}

    reproduces the given quantities, and both sides carry the same units.

Answer:
V=1.0014 m/sV = 1.0014\ \text{m/s}

Why the other options are there

  • 2.0027 — kept a factor of two that cancels in the correct rearrangement.
  • 0.5007 — dropped that same factor in the other direction.
  • 1.1015 — rounded an intermediate value before the final step.

Reference: FE Handbook — Hazen-Williams Equation

Example 10
Hazen-Williams equation — solve for Hazen-Williams coefficient (case 5) — Hazen-Williams Equation (10)

the Hazen-Williams equation for a water distribution pipeline Given hydraulic radius (R_H) = 0.1800 m; slope of energy grade line (S) = 0.0045 m/m; velocity (V) = 0.7000 m/s, determine the Hazen-Williams coefficient (C_HW).

Given

  • hydraulicradius(RH)=0.1800mhydraulic radius (R_H) = 0.1800 m
  • slopeofenergygradeline(S)=0.0045m/mslope of energy grade line (S) = 0.0045 m/m
  • velocity(V)=0.7000m/svelocity (V) = 0.7000 m/s

Find

Hazen-Williams coefficient (C_HW)

Start with the thinking

  • The governing relation printed in this handbook section is Hazen-Williams equation.
  • Everything except C_HW is given, so isolate C_HW symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The Hazen-Williams equation estimates flow velocity in a pipeline given its roughness coefficient and slope.
D₁=150D₂=150VS

Figure 10 — schematic for Hazen-Williams equation — solve for Hazen-Williams coefficient (case 5) — Hazen-Williams Equation (10)

Step-by-step solution

  1. Step 1 — State the governing relation:

    V=0.849 CHWRH0.63S0.54V = 0.849\, C_{HW} R_H^{0.63} S^{0.54}
  2. Step 2 — Rearrange the relation so that C_HW stands alone on the left-hand side.

  3. Step 3 — List the givens: hydraulic radius (R_H) = 0.1800 m, slope of energy grade line (S) = 0.0045 m/m, velocity (V) = 0.7000 m/s.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    CHW=44.9401C_{HW} = 44.9401
  6. Step 6 — Check: returning C_HW = 44.9401 to

    V=0.849 CHWRH0.63S0.54V = 0.849\, C_{HW} R_H^{0.63} S^{0.54}

    reproduces the given quantities, and both sides carry the same units.

Answer:
CHW=44.9401C_{HW} = 44.9401

Why the other options are there

  • 89.8802 — kept a factor of two that cancels in the correct rearrangement.
  • 22.4700 — dropped that same factor in the other direction.
  • 49.4341 — rounded an intermediate value before the final step.

Reference: FE Handbook — Hazen-Williams Equation

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