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Two pumps can fill a water tank in 45 minutes when working together.
Alone, the second pump takes 3 times longer than the first to fill the tank.
How long does it take the first pump alone to fill the tank?
Let x = time required for the first pump to fill the tank alone
3x = time required for the 2nd pump to do it alone
Write an equation of them working together; let the full tank = 1
Each pump will do a fraction of the job and will equal 1 when added together
Multiply equation by 3x, results
3(45) + 45 = 3x
135 + 45 = 3x
180 = 3x
x = 60 min for pump 1 alone
Check solution; (2nd pump requires 3*60 = 180 min alone)
.75 + .25 = 1; confirms our solution