Question

1) A can complete a piece of work in 10 days, B can do it in 12 days and C can
do it in 15 days. In how many days will they finish the work if they work
together?​

Answer 1

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A and B together can do a piece of work in 10 days, while B and C together can do it in 12 days and C and A together in 15 days. In how many days C would complete it alone? Hence C will finish the work in 40 days. So option [C] is correct answer.