Question

A can do a piece of work in 10 days and b can do it in 15 days and c can do it 20 days. they started the work together and a leaves after 2 days and b leaves after 4 days from the beginning. how many days needed to complete the work

Answer 1

- after 2 days A had done 2/10 of the work and after 4 days B had done 4/15 of the work.

- work to be done by C = 1 - (2/10 + 4/15)
                                     = 8/15
- if C does 1/20 of the work in 1 days;
  8/15 of the work = 8/15 divided by 1/20
                            = 10 2/3 days.

- therefore it took 10 and 2/3 days to complete the work.