A, B and C can do a piece of work in 7 days, 14 days and 28 days respectively.…
2023
A, B and C can do a piece of work in 7 days, 14 days and 28 days respectively. How long will they taken, if all the three work together?
- A.
3 days
- B.
4 days
- C.
5 days
- D.
6 days
Attempted by 71 students.
Show answer & explanation
Correct answer: B
Key idea: add individual work rates (work per day) and invert the total rate to get the time.
Compute individual rates: A = 1/7 work/day, B = 1/14 work/day, C = 1/28 work/day.
Add the rates: 1/7 + 1/14 + 1/28 = (4 + 2 + 1) / 28 = 7/28 = 1/4 work/day.
Time to finish = 1 ÷ (total rate) = 1 ÷ (1/4) = 4 days.
Answer: They will finish the work in 4 days when all three work together.