Question

6. A and B separately do a work in 10 and 15 days respectively. They worked together
for some days and then A completed the remaining work in 5 days. For how many
days had A and B worked together?
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Answer 1

Given

A can do work in 10 days = work done in 1 day is w/10

let W be total work

B can do work in 15 days=work done in 1 day is w/15

let n be the number of days they both work together

work done by together in a day =w/10 +w/15 =w/6

= n * W/6+5*w/10=w

=n*w/6=w/2

=n=3

hence the number of days they worked together is 3 days