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A, B, C can individually complete a work in 20 days, 15 days, 12 days respectively. B and C start the work and they worked for 3 days and left. Then the number of days required by A to finish the remaining work is
Solution
A, B, C can individually complete a work in 20 days, 15 days, 12 days respectively
Efficiency of (A + B + C) = $$\left(\frac{1}{20}+\frac{1}{15}\ +\frac{1}{12}\right)$$ = $$\left(\frac{3+4+5}{60}\right)\ =\ \frac{12}{60\ }$$
Efficiency of only (B + C) =$$\left(\frac{1}{15}+\frac{1}{12}\right)$$ = $$\left(\frac{4+5}{60}\right)\ = \ \frac{9}{60\ }$$
So efficiency of A = $$\frac{12}{60}-\frac{9}{60}\ =\ \frac{3}{60}$$
While working, all 3 work for 3 days.
So work completed in 3 days = $$3\ \times\ \frac{12}{60}\ =\ \frac{36}{60}$$
Work Remaining = $$1\ -\frac{36}{60}\ =\ \frac{24}{60}$$
If A works alone @ $$\frac{3}{60}$$ work per day. = $$\frac{\left(\frac{24}{60}\right)}{\left(\frac{3}{60}\right)}$$ = 8 days.
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