Mark (✓) against the correct answer:
Question:

Mark (✓) against the correct answer:

A works twice as fast as B. If both of them can together finish a peice of work in 12 hours, then B alone can do it in

(a) 24 hours

(b) 27 hours

(c) 36 hours

(d) 18 hours

Solution:

(c) 36 hours

Suppose B take s x hour s to complete the work.

$\therefore$ B’s 1 hour work $=\frac{1}{\mathrm{x}}$

A works twice as fast as B.

$\therefore$ A’s 1 hour work $=\frac{2}{x}$

$\frac{1}{12}=\frac{1}{\mathrm{x}}+\frac{2}{\mathrm{x}}=\frac{3}{\mathrm{x}}$

$\Rightarrow \mathrm{x}=36$ hours