Question 186956
here is another problem i have been trying to figure out how to do. 
john can fill the pool in 30 min, sue can fill the pool in 45 min, and sam can fill it in 90 min how long would it take all three of them to fill the pool together 
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You have to find how much of the pool each can fill in a minute, then add those.
John can fill 1/30 per minute, sue 1/45 and sam 1/90
1/30 + 1/45 + 1/90 = 6/90 = 1/15 of the pool per minute together
Then, it takes 15 minutes.