SOLUTION: if john build a wall in 5 hours and mark build the same wall but in 8 hours then if john and mark will work together to build one wall, So what the time requested to build it ?

Question 940079: if john build a wall in 5 hours and mark build the same wall but in 8 hours then if john and mark will work together to build one wall, So what the time requested to build it ?
Answer by KMST(5328) (Show Source): You can put this solution on YOUR website!
John can build 1/5 of the wall per hour.
Mark can build 1/8 of the wall per hour.
Working together, each hour they can build
1/5+1/8=8/40+5/40=13/40
of the wall.
So, working together, it should take them
hours.
Since 1/13 of an hour is 60/13 minutes,
which is a little more than 4.6 minutes, but less than 5 minutes,
I think they should estimate that it will take them
3 hours and 5 minutes.
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