A can do piece of work in 6 days and B can do piece of work in 12 days. If both of them worked together in how many days they can finished?

A can complete a piece of work in 6 days

B  can complete a piece of work in 12 days

A’s 1day work $=\frac{1}{6}$

B’s 1 day work $=\frac{1}{12}$

$(A+B)\text{'}s$ I day work $=\frac{1}{6}+\frac{1}{12}$

$=\frac{2+1}{12}=\frac{3}{12}=\frac{1}{4}$

$\therefore$ A & B all completed work in together 4 days