Question : A, B and C can do a piece of work in 20 days, 30 days and 60 days respectively. If A works daily and on every third day B and C also work with A, then in how many days, will the work be completed?
Option 1: 21
Option 2: 18
Option 3: 12
Option 4: 15
Correct Answer: 15
Solution :
The rates at which A, B, and C can complete the work are $\frac{1}{20}$, $\frac{1}{30}$, and $\frac{1}{60}$ of the work per day, respectively.
In a cycle of three days, A works for three days, B works for one day, and C works for one day. So, the total work done in three days is $=3\times\frac{1}{20} + 1\times\frac{1}{30} + 1\times\frac{1}{60}$
$ = \frac{3}{20} + \frac{1}{30} + \frac{1}{60}=\frac{3}{20} + \frac{1}{30} + \frac{1}{60}$
$ = \frac{9}{60} + \frac{2}{60} + \frac{1}{60} $
$= \frac{12}{60}$
$= \frac{1}{5}$
So, in three days, they complete $\frac{1}{5}$ of the work.
Therefore, the work will be completed in $5 \times 3 = 15$ days.
Hence, the correct answer is 15.
Related Questions
Know More about
Staff Selection Commission Sub Inspector ...
Result | Eligibility | Application | Selection Process | Cutoff | Admit Card | Preparation Tips
Get Updates Brochure
Your Staff Selection Commission Sub Inspector Exam brochure has been successfully mailed to your registered email id “”.
