SOLUTION: how to solve sam can do a work in 3 days and john can do that work in 5 days,how many days they will take to finish that work if work togather?

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Question 297627: how to solve sam can do a work in 3 days and john can do that work in 5 days,how many days they will take to finish that work if work togather?
Found 2 solutions by vleith, richwmiller:
Answer by vleith(2983) (Show Source):
You can put this solution on YOUR website!
The way I like to do these is to look at each one's daily rate. Then add their daily rate to see how they can work together.
So Sam can do 1/3 of the job in a day (so he takes 3 days to do the job alone)
John can do 1/5 of the job in a day (it take him 5 days to do the whole thing)
Together, their daily rate is = =
So they can do over half the job in a ay
To do the whole job

1 job is a whole job done once

So working together they can do the job in 1 and 7/8's days.
Make sense now?

Answer by richwmiller(17219) (Show Source):
You can put this solution on YOUR website!
x/3+x/5=1
x is a the time it takes them working together
1 is one job
x/3 is the part of the job that Sam does
x/5 is the part of the job that John does
multiply by 15
5x+3x=15
8x=15
x=15/8
x= 1 7/8 days to do the job together
7/8*24=21 hours
x=1 day and 21 hours to do the job together
check
15/8/3+15/8/5=1
5/8+3/8=1
Sam does 5/8 of the job and john does 3/8
ok