NIFT UG 2019 Question Paper with solutions

Since, $\mathit{X}$ is thrice as good a workman as $\mathit{Y}$.
$\therefore$ Ratio in their working efficiency $=3:1$
Then, ratio between the time taken by them to complete the work $=1:3$
Let $\mathit{X}$ can complete the work in $\mathit{X}$ days and $\mathit{Y}$ in $3\mathit{x}$ days.
According to the question,
$3\mathit{x}-\mathit{x}=40\Rightarrow 2\mathit{x}=40$
$\Rightarrow \mathit{x}=20$
$\therefore$ Working efficiency of both
Hence, they can do the work together in 15 days.