Question 130

A and B together can dig a trench in 12 days, which A alone can dig in 28 days; B alone can dig it in

Solution

let the amount of work equivalent to dig a trench be 84 units

Given that (A+B) completes the work in 12 days

So (A+B)'s 1 day work = 7 units

It is given that A can complete the whole work in = 28 days

A's 1 day work = 3 units

3 + B's 1 day work = 7

B's 1 day work = 4 units

hence B will take = $$\frac{84}{4}$$ = 21 days to complete the work alone

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