A and B can complete a work in 10 and 12 days respectively. A and B start working together and after 3 days, A left the work. Find in how many days work will be completed.

\(8\frac{2}{5}\)

Total work = Efficiency × Number of days

work done by ( A + B ) in 3 days = ( 6R + 5R ) × 3 = 33R

Remaining work = 60R - 33R = 27R

Time taken by B to complete the remaining work = \(\frac{27R}{5R}\)

= \(\frac{27}{5}\)

total time taken in doing whole work = 3 + \(\frac{27}{5}\)

= \(\frac{42}{5}\)  = 8\(\frac{2}{5}\)