Question

A’ can do a piece of work in 20 days which ‘B’ alone can do in 12 days. ‘B’ worked at it for 9
days then ‘A’ can finish the remaining work in :

Answer 1

In 1 day A can do 1/20 part of the work
In 1 day B can do 1/12 part of the work

By working for 9 days B can do
$\frac{1}{12} \times 9 = \frac{3}{4} \: \: \: part \: of \: the \: work \\ now \: 1 - \frac{3}{4} part \: of \: the \: work \: is \: left \\ \frac{1}{4} part \: is \: left$
A can do it in 1/4 / 1/20 days
A can do it in 5 days