SOLUTION: If one person can fill a pool in 30min another in 45min and another in 90min how long would it take if they all work together. i know the answer is 15 but i dont know the equation

Question 477134: If one person can fill a pool in 30min another in 45min and another in 90min how long would it take if they all work together. i know the answer is 15 but i dont know the equation used to get the answer.
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
If one person can fill a pool in 30min another in 45min and another in 90min how long would it take if they all work together. i know the answer is 15 but i dont know the equation used to get the answer.
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Equation:
rate + rate + rate = together rate
1/30 + 1/45 + 1/90 = 1/x
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Multiply thru by 90x to get:
3x + 2x + x = 90
6x = 90
x = 15 minutes
====================
Cheers,
Stan H.
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