Question

Ram can complete a work in 10 hours, Ajit in 12 hours and Suresh in 15 hours. All of them began the work together, but Ram had to leave the work after 2 hours of the start and Ajit left 3 hours before the completion of the work. How long did the work last? ___ hours

Answer 1

In 1 hour Ram can do $10\%$ of the work, Ajit can do $\frac{100}{12}\%$ of the work and Suresh can do $\frac{100}{15}\%$ of the work.

So, total number of hours = 2 + 2 + 3 = 7 hours.