SOLUTION: An oil tanker can be filled in 18h using one pump and 15h using a different pump. If both pumps are used, how long would it take to fill the tanker?

Question 249329: An oil tanker can be filled in 18h using one pump and 15h using a different pump. If both pumps are used, how long would it take to fill the tanker?
Answer by Alan3354(69443) (Show Source): You can put this solution on YOUR website!
An oil tanker can be filled in 18h using one pump and 15h using a different pump. If both pumps are used, how long would it take to fill the tanker?
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If you add 15 and 18 it's 33 hours. That can't be right.
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One pump does 1/15 of the tanker per hour.
The other does 1/18 per hour.
Together they do 1/15 + 1/18 per hour = 6/90 + 5/90
= 11/90 per hour
--> 90/11 hours per tanker
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There's a shortcut, product/sum
15*18/(15+18) = 270/33
= 90/11 hours
=~ 8.18 hours
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