A and B together can dig a trench in 12 days, which A alone can dig in 28 days, B alone can dig it in :
A and B together can dig a trench in 12 days, which A alone can dig in 28 days, B alone can dig it in :
[A]20 days
[B]21 days
[C]22 days
[D]23 days
21 days
B’s 1 day’s work = (A + B)’s 1 day’s work – A’s 1 day’s work
$latex \therefore \frac{1}{12}-\frac{1}{28} = \frac{7-3}{84}&s=1$
$latex = \frac{4}{84} = \frac{1}{21}&s=1$
∴ Required time = 21 days.
Hence option [B] is correct answer.