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