A can complete a piece of work in 18 days, B in 20 days and C in 30 days, B and C together start the work and forced to leave after 2 days. The time taken by A alone to complete the remaining work is:
A. 10 days
B. 12 days
C. 15 days
D. 16 days
Answer: Option C
Solution(By Examveda Team)
1st Method: $$\eqalign{ & \left( {B + C} \right)\,2\,{\text{days}}\,{\text{work}} \cr & = 2 \times \left( {\frac{1}{{20}} + \frac{1}{{30}}} \right) \cr & = 2 \times {\frac{{3 + 2}}{{60}}} \cr & = \frac{1}{6}{\text{part}} \cr & {\text{Remaining}}\,{\text{work}} \cr & = 1 - \frac{1}{6} \cr & = \frac{5}{6}\text{part} \cr & {\text{A's}}\,{\text{one}}\,{\text{day's}}\,{\text{work}} \cr & = \frac{1}{{18}}{\text{part}} \cr & {\text{Time taken to complete the work}} \cr & = \frac{{ {\frac{5}{6}} }}{{ {\frac{1}{{18}}} }}\,{\text{days}} \cr & {\text{Hence,}} \cr & {\text{Time taken to complete the work}} \cr & = {\frac{5}{6}} \times 18 \cr & = 15\,{\text{days}} \cr} $$2nd Method: % of work B completes in one day = $$\frac{{100}}{{20}}$$ = 5%; % of work C completes in one day = $$\frac{{100}}{{30}}$$ = 3.33%; % of work (A + B) completes together in one day = 5 + 3.33 = 8.33%; % work (A + B) completes together in 2 days = 8.66 × 2 = 16.66%; Remaining work = 100 - 16.66 = 83.34%; % of work A completes in 1 day = $$\frac{{100}}{{18}}$$ = 5.55% Time taken to complete the remaining work by A = $$\frac{{83.34}}{{5.55}}$$
= 15 days
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Comments ( 2 )
Related Questions on Time and Work
A. 18 days
B. 24 days
C. 30 days
D. 40 days
2nd method requires correction.
% WORK (B+C)=5+3.33=8.33%
2DAYS WORK =8.33X2=16.66%
REMAINING WORK =100-16.66=84.34%
A CAN DO THE WORK IN =83.34/5.55= 15DAYS
B in a day does 9 unit work and C does 6 unit of work.
B+C in 2 days = 18 + 12 =30 units
remaining unit = 180 - 30 =150
since A in 1 day does 10 units work
to complete 150 unit remaining work he need 15 days.