Question

A,B,C can do a piece of work in 15 days . B alone can do it in 30 days and C can do it in 40 days . find how long will A take to that work?

Answer 1

B can do the work in 30 days

C can do work in 40 days

given A and B and C can work in 15 days

A+B+C=15

A+30+40=15

Hence, A can work in 55 days

Answer 2

Given, ABC can work in = 15 days

ABC 1 day work = 1/15

B alone can do it in = 30

B's 1 day work = 1/30

C alone can do it in = 40

C's 1 day work = 1/40

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Then, A's 1 day work = 1/ABC - 1/B - 1/C

= 1/15 - 1/30 - 1/40

= (8-4-3) / 120

= 1/120

A will do whole work alone in 120 days.

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