Question

. A alone can complete a piece of work in 6 days and B alone can complete the same piece of work in 12 days. In how many days can A and B together complete the same piece of work

Answer 1

In 1 day A can finish part of work=1/6
In 1 day B can finish part of work=1/12
Both will finish part of work in 1 day=1/6+1/12
=(2+1)/12
=1/4work
So work will complete in 4 days

Answer 2

A can do a piece of work in 6 days.
$1day \: work \: of \: a = \frac{1}{6}$
B can do a piece of work in 12 days.
$1days \ \: work \:of \: b = \frac{1}{12}$
(A+B)'s 1 day work=
$\frac{1}{6} + \frac{1}{12} \\ \frac{2 + 1}{12} \\ \frac{3}{12} = 4$
Hence,
Together they can complete it in 4 days..