A can complete a job in 30 days, B in 40 days and C in 50 days. B and C start the work and are forced to leave after 4 days. The time taken to complete the remaining work is

A can do job in 1 day $=\frac{1}{30}$

B can do job in 1 day $=\frac{1}{40}$

C can do job in 1 day $=\frac{1}{50}$

$B+C=\frac{1}{40}+\frac{1}{50}=\frac{5+4}{200}=\frac{9}{200}$

$Forworked4days=\frac{9}{200}\times 4=\frac{9}{50}work\Rightarrow \text{Remaining}=\frac{41}{50}$

$Acandowork=\frac{41}{50}\times 30=\frac{123}{5}=24.6days$