Question 61

A can do a work in 20 days and B in 50 days. If they work on it together for 5 days, then what fraction of work is left?

Solution

Let total work to be done = 100 units

A's efficiency = $$\frac{100}{20} = 5$$ units/day

B's efficiency = $$\frac{100}{50} = 2$$ units/day

(A + B)'s 1 day's work together = 5 + 2 = 7 units/day

Now, work done by them together in 5 days = $$5 \times 7 = 35$$ units

=> Work left = 100 - 35 = 65 units

$$\therefore$$ Fraction of work that is left = $$\frac{65}{100} = \frac{13}{20}$$

=> Ans - (A)

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