A alone can complete a work in 12 days. A and B together can complete it in 8 days. How long will B alone take to complete the work?

A alone can complete a work in 12 days. A and B together can complete it in 8 days. How long will B alone take to complete the work?
[A]20 days
[B]24 days
[C]16 days
[D]18 days

24 days
A’s one day’s work $= \frac{1}{12}$
(A + B)’s one day’s work $= \frac{1}{8}$
∴ B’s one day’s work =
$= \frac{1}{8} - \frac{1}{12} = \frac{3-2}{24} = \frac{1}{24}$
∴ B alone can do the work in 24 days.
Hence option [B] is the right answer.