A can do a piece of work in 60 days. He works for 6 days and then B alone finishes the remaining  work in 36 days. The two together can finish the work in

Solution: A can do a piece of  work $=60days=\frac{1}{60}$

A worked for 6 days $=\frac{1}{60}\times 6=\frac{1}{10}ofworkcompleted$

$Bhastodo\frac{9}{10}ofthework\Rightarrow \frac{10}{9}\times 4=40days$

$A+B\Rightarrow \frac{1}{60}+\frac{1}{40}=\frac{2+3}{120}=\frac{1}{24}\Rightarrow 24days$