SSC CGL Tier II 25 Oct 2015 Paper 1

(2) (P + Q)’s 1 day’s work $=\frac{1}{6}$
(Q + R)’s 1 day’s work $=\frac{7}{60}$
Let P alone do the work in x days.
According to the question,
$\frac{3}{\mathit{x}}+\frac{6\times 7}{60}=1$
$\Rightarrow \frac{3}{\mathit{x}}=1-\frac{7}{10}=\frac{3}{10}$
⇒ x = 10 days
∴ Q’s 1 day’s work $=\frac{1}{6}-\frac{1}{10}=\frac{5-3}{30}=\frac{1}{15}$
R’s 1 day’s work $=\frac{7}{60}-\frac{1}{15}=\frac{7-4}{60}=\frac{1}{20}$
∴ Time taken by R = 20 days
∴ Required answer = 20 – 10 = 10 days