One hose can fill and goldfish pond in 28 minutes, and two hoses came for the same pond in 20 minutes. Find how long it takes a second holes alone to fill the pond

Correct  t₂ = 70 minutes

Step-by-step explanation:

Given:

t₁ = 28 minutes  and t₁₂ = 20 minutes, t₂ = ?

The necessary equation for this situation is:

1/t₁ + 1/t₂ = 1/t₁₂  => 1/28 + 1/t₂ = 1/20 => (28 + t₂)/ 28 t₂ = 1/20 =>

28 t₂ = (28 + t₂) · 20 = 20 t₂ + 560 => 28 t₂ - 20 t₂ = 560 =>

8 t₂ = 560 => t₂ = 560/8 = 70 minutes

t₂ = 70 minutes

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