Question 83

A can do a work in 15 days and B in 20 days. If they work on it together for 6 days, then what fraction of work is left?

Solution

Let total work to be done = 60 units

A's efficiency = $$\frac{60}{15} = 4$$ units/day

B's efficiency = $$\frac{60}{20} = 3$$ units/day

=> (A + B)'s 1 day's work = 4 + 3 = 7 units/day

Work done by A and B together in 6 days = $$6 \times 7 = 42$$ units

=> Work left = 60 - 42 = 18 units

$$\therefore$$ Fraction of work that is left = $$\frac{18}{60} = \frac{3}{10}$$

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