Question

A and b can together do a piece of work in 15 days.b alone can do it in 20 days .in how many days can a alone do it

Answer 1

A's 1 day work +B's 1 day work = 1/15

So, A's 1 day work = 1/15 - 1/20

= 1/60

So, A can do the same work in 60 days

Answer 2

A and B → 15 days

A → 20days

So, let's take LCM of 15 and 20. That's 60.

This 60 unit is the total work to be done.

So, A and B do (60/15) = 4 unit work/day …(1)

And, A does (60/20) = 3 unit work/day …(2)

(1)-(2) gives

B does (4–3)= 1 unit/day

So, Total days req. = (Total work)/unit per day

i.e, B can do it in (60/1)=60 days.