Question

A and B can polish the floors of a building in 12 days. A alone can do 1/5 of this job in 4 days. In how many days can B alone polish the floors?

Answer 1

days for A to do complete job = 5 x 4 =20
let days for B to do complete job = X

work done by A in 1 day = 1/20
work done by B in 1 day = 1/X

days for both A and B to do complete job =12

work done by both A and B in 1 day =
(1/20) + (1/X) = 1/12
(X+20)/20X=1/12
12X+240=20X
8X=240
X=30days