A and B together can do a work in 6 days. They worked for 3 days and then C joined them. As a result the work could be done in 5 days. If A, B and C work together from the beginning, then in how many days will the work be done?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 4
Work is measured as a fraction of the whole job: a group that finishes it in n days does \(\frac{1}{n}\) of it each day.
A and B do \(\frac{1}{6}\) of the work a day, so in 3 days they finish \(\frac{3}{6}=\frac{1}{2}\) of it
The work ended on day 5, so A, B and C together did the other \(\frac{1}{2}\) in the remaining 2 days
A, B and C do \(\frac{1}{2}\div2=\frac{1}{4}\) of the work a day
Working together from the start, they need 4 days