Question 91

A can do a work in 20 days and B in 10 days. If they work on it together for 5 days, then what fraction of work is left.

Solution

Let total work to be done = 20 units

A's efficiency = $$\frac{20}{20} = 1$$ unit/day

B's efficiency = $$\frac{20}{10} = 2$$ units/day

(A + B)'s 1 day's work together = 1 + 2 = 3 units/day

Now, work done by them together in 5 days = $$5 \times 3 = 15$$ units

=> Work left = 20 - 15 = 5 units

$$\therefore$$ Fraction of work that is left = $$\frac{5}{20} = \frac{1}{4}$$

=> Ans - (B)

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