Question 55

A can do a work in 15 days and B in 9 days. If they work on it together for 5 days, then what fraction of work is left?

Solution

Let total work to be done = 45 units

A's efficiency = $$\frac{45}{15} = 3$$ units/day

B's efficiency = $$\frac{45}{9} = 5$$ units/day

(A + B)'s 1 day's work = 3 + 5 = 8 units/day

Work done by them together in 5 days = $$8 \times 5 = 40$$ units

Work left = 45 - 40 = 5 units

$$\therefore$$ Fraction of work that is left = $$\frac{5}{45} = \frac{1}{9}$$

=> Ans - (D)

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