Math Question

[jeppuda]

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Can someone explain this to me?

Jim can fill a pool carrying bucks of water in 30 minutes. Sue can do the same job in 45 minutes. Tony can do the same job in 1 ½ hours. How quickly can all three fill the pool together? 12 minutes 15 minutes 21 minutes 23 minutes 28 minutes


Answer is 15....I found this question online...It only gives answers and not explanations...I do not want to buy another study guide for DAT...thanks

 

[mshopeful]

There's a formula:
1/t1 + 1/t2 + 1/t3 = 1/T

t1, t2, t3 being the time each person takes, and T=total time for all three.

1/30 + 1/45 + 1/90 = 1/T
Solve, T = 15

 

[Streetwolf]

The formula works for any number of people... so for 2 people it's 1/t1 + 1/t2 = 1/T

You see 3 people there.

For 4 people you have 1/t1 + 1/t2+ 1/t3 + 1/t4 = 1/T

And so forth.