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Question
A, B and C can do a piece of work in 12, 15 and 20 days respectively. How long will they take to do it working together?
Solution
A can do a piece of work in 12 days
B can do the same work in 15 days
C can do the same work in 20 days
∴ A's 1 day's work = `1/12`
B's 1 day's work = `1/15`
C's 1 day's work = `1/20`
∴ (A + B + C)'s together 1 day's work
`= 1/12 + 1/15 + 1/20`
`= (5 + 4 + 3)/60 = 12/60 = 1/5`
∴ they can do the work in 5 days.
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