SSC CHSL 11 Aug 2021 Shift 2 Paper

Given, A completes $20\%$ of the work in 5 days.
$\therefore$ Total time taken to complete the whole work by $\mathit{A}=\frac{5}{20}\times 100=25$ days and $\mathit{B}$ completes $\frac{1}{3}$ th of the work in 5 days.
$\therefore$ Total time taken to complete the whole work by $\mathit{B}=5\times 3=15$ days
According to the question, 3 days work
$=\frac{3}{25}+\frac{3}{15}=\frac{3}{25}+\frac{1}{5}=\frac{3+5}{25}=\frac{8}{25}$
Remaining work $=1-\frac{8}{25}$

$\therefore$ Total number of days needed for complete the work $=\left(25\times \frac{17}{25}+3\right)$ days $=20$ days