Question 291755
Jim can fill a pool carrying buckets of water in 30 minutes. Sue can do the same job in 45 minutes. Tony can do the same job in 1 1/2 hours. How quickly can all three fill the pool together? 
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Use the inverses, pools filled per hour, then you can add them.
Jim does 1/30 of the pool per minute.
Sue does 1/45
Tony does 1/90
Together, 1/30 + 1/45 + 1/90 = 3/90 + 2/90 + 1/90 = 6/90 = 1/15
1/15 of a pool per minute --> 15 mins per pool