A can do a piece of work in 8 days. If

A can do a piece of work in 8 days. If B can do it in 10 days, in how many days can
both working together do it?

Solution
1
Let x= the required number of days, then = the part of the work both can do in 1
x
day;
1 1
= the part of the work A can do in 1 day; = the part of the work B can do in 1
x x
day:
1 1 1 9
= + , or
x 8 10 10
40 4
Solving, x = = 4 , the required number of days.
9 9
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