P can do a piece of work in 20 days and Q can do the same piece of work in 60 days. They start working together and work for 5 days and then both leave the work. R alone finishes the remaining work in 10 days. In how many days will R alone finish the whole work?

P can do a piece of work in 20 days and Q can do the same piece of work in 60 days. They start working together and work for 5 days and then both leave the work. R alone finishes the remaining work in 10 days. In how many days will R alone finish the whole work? Correct Answer 15

Work done by P in 1 day = 1/20

Work done by Q in 1 day = 1/60

Work done P and Q in 1 day = 1/20 + 1/60 = 1/15

Work done by P and Q in 5 days = 5 ⨯ 1/15 = 1/3

∴ P and Q finished 1/3rd of the work in 5 days.

R finished 2/3rd of the work in 10 days

2/3 work = 10 days

1 work = 10 × (3/2) = 15 days

∴ R will finish the whole work in 15 days.

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