A can finish a work in 18 days and B can do the same work in half the time taken by A. Then, working together, what part of the same work they can finish in a day ?

\par A's one day's work =  \frac{1}{18}

\par B's one day's work =  \frac{1}{9}

\par (A+B)'s one day's work = \frac{1}{18}+\frac{1}{9} = \frac{1}{6}