Question

A did 3/4 of a work in 30 days. Then B joined and the remaining is finished in 4 days. In how many days will B alone finishes the work?

Answer 1

pary of work done in 30 days=3/4
part of work done in 1 day= 3/4×1/30=1/40
Remaining work is 1/4
work done by both in 4 days = 1/4
work done by both in 1 day = 1/4×1/4=1/16
Part of work of work done by B in 1 day= 1/16-1/40 =3/80
B can do alone in 3/80×4=3/20 days

Answer 2

as A did 3/4 work in 30 days he will complete alone in 40 days
one day work of A is 1/40
let work of B is x
then
1/x + 1/40 = 1/4
=> x = 40/9