SSC CHSL Model Paper 15

B’s work =100 units
C’s work = 80 units
A’s work =140 units
∴ Ratio of the work of A, B and C = 140 : 100 : 80 = 7 : 5 : 4
∴ Ratio of time taken $=\frac{1}{7}:\frac{1}{5}:\frac{1}{4}$ $=20:28:35$
$\therefore \frac{1}{20\mathit{x}}+\frac{1}{28\mathit{x}}+\frac{1}{35\mathit{x}}=\frac{1}{15}$
$\Rightarrow \frac{7+5+4}{140\mathit{x}}=\frac{1}{15}$
$\Rightarrow 140\mathit{x}=15\times 16$
$\Rightarrow \mathit{x}=\frac{12}{7}$
∴ Time taken by B in doing 1 work $=\frac{12}{7}\times 28=48\mathrm{days}$
∴ Time taken by B in doing 75% work $=\frac{3}{4}\times 48=36\mathrm{days}$