Question

Three people A, B and C can do a job alone in 10 days, 12 days and 15 days respectively. In how many days they can finish the job working together?

• A. 4 days
• B. $\frac{7}{2}$ days
• C. 6 days
• D. $2\frac{1}{3}$ days

Answer 1

The correct option is A 4 days

Amount of work that can be done in a day by A, B and C are $\frac{1}{10},\frac{1}{12}$ and $\frac{1}{15}$ respectively.
One day worth of work that can be done if they work together is
$=(\frac{1}{10}+\frac{1}{12}+\frac{1}{15})=\frac{15}{60}=\frac{1}{4}$
$\therefore$ Time required to complete the job
$=\frac{1}{\frac{1}{4}}=4days$.