a) $${\text{5}}\frac{1}{5}{\text{ days}}$$
b) $${\text{6}}\frac{1}{4}{\text{ days}}$$
c) $${\text{7}}\frac{1}{2}{\text{ days}}$$
d) $${\text{8}}\frac{3}{4}{\text{ days}}$$
Answer: c
Explanation: L.C.M. of Total Work = 15
One day work of A + B = $$\frac{{15}}{5}$$ = 3 unit/day
One day work of (2A + B) = $$\frac{{15}}{3}$$ = 5 unit/day
Assume A’s efficiency is 2 units, B’s is 1 unit.
It satisfies the equation of both cases
Actual efficiency of A is 2 units/day
A alone can complete the work in
$$\eqalign{
& = \frac{{{\text{Total work}}}}{{{\text{Efficiency}}}} \cr
& = \frac{{15}}{2} \cr
& = 7\frac{1}{2}{\text{days}} \cr} $$
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