Question:
A can do a piece of work in 10 days while B alone can do it in 15 days. In how many days can both finish the same work?
Solution:
A can do a piece of work in 10 days.
A's 1 day work $=\frac{1}{10}$
B can do a piece of work in 15 days.
B's 1 day work $=\frac{1}{15}$
$(\mathrm{A}+\mathrm{B})$ 's 1 day work $=\frac{1}{10}+\frac{1}{15}=\frac{3+2}{30}=\frac{5}{30}=\frac{1}{6}$
$\mathrm{A}$ and $\mathrm{B}$ working together can complete the work in 6 days.