Question 27

A can finish a work in 18 days and B in 36 days. If they work on it together for 9 days, then what percent of work is left?

Solution

Let total work to be done = 36 units

A's efficiency = $$\frac{36}{18} = 2$$ units/day

B's efficiency = $$\frac{36}{36} = 1$$ unit/day

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

Now, work done by them together in 9 days = $$9 \times 3 = 27$$ units

=> Work left = 36 - 27 = 9 units

$$\therefore$$ Percent of work that is left = $$\frac{9}{36}\times100 = 25\%$$

=> Ans - (D)

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