SSC CHSL 5 Aug 2021 Shift 3 Paper

Work done by $\mathit{A}$ and $\mathit{B}$ together in

$=\frac{50+40}{100}=\frac{90}{100}=\frac{9}{10}$
$\therefore$ Remaining work $=1-\frac{9}{10}=\frac{1}{10}$
Since, $\mathit{C}$ alone completed the remaining work in 10 days.
$\therefore$ can complete the whole work in $10\times 10=100$ days
Now, work done by $\mathit{A},\mathit{B}$ and $\mathit{C}$ together in 1 days
$=\frac{1}{20}+\frac{1}{25}+\frac{1}{100}$
$=\frac{5+4+1}{100}=\frac{10}{100}=\frac{1}{10}$
$\therefore$ If they work together, they will complete the whole work in 10 days.