SOLUTION: not sure if in right category but when the question is like jill does this in 30 min bob does it in 45 sue takes an hour and a half how long does it take all of them to do it t

Question 136731: not sure if in right category
but when the question is like jill does this in 30 min
bob does it in 45
sue takes an hour and a half
how long does it take all of them to do it together
i have no idea how to solve this problem
Found 2 solutions by stanbon, solver91311:
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
jill does this in 30 min
bob does it in 45
sue takes an hour and a half
how long does it take all of them to do it together
---------------
You have to realize you cannot add times; you have to add rates.
--------------
Jill DATA:
Time = 30 min/job ; Rate = 1/30 job/min
----------------
Bob DATA:
Time = 45 min/job ; Rate = 1/45 job/min
-----------------
Sue DATA:
Time = 90 min ; Rate = 1/90 job/min
------------------
Together DATA:
Time = x min/job ; Rate = 1/x job/min
------------------
EQUATION:
rate + rate + rate = together rate
1/30 + 1/45 + 1/90 = 1/x
Multiply thru by 90x to get:
3x + 2x + x = 90
6x = 90
x = 15 (amount of time to do the job if they work together)
=====================
Cheers,
Stan H.

Answer by solver91311(24713) (Show Source): You can put this solution on YOUR website!
Jill does the job in 30 minutes or 1/2 hour. So turn the fraction over and Jill can do 2/1 or 2 jobs per hour.

Bob does the job in 45 minutes or 3/4 hour. Bob can do 4/3 job per hour.

Sue does the job in 3/2 hour. Sue can do 2/3 job per hour.

2 plus 4/3 plus 2/3 = 6/3 + 4/3 + 2/3 = 12/3 = 4 jobs per hour working together.

Turn the fraction (4/1) over again, and together they can do the job once in 1/4 hour or 15 minutes.
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