A, B and C can do a work in 10, 12 and 15 days respectively. In how many days will the work be completed if B is assisted by both A and C on every third day?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 8
Taking the whole work as the LCM of 10, 12 and 15, that is, 60 units, each person’s daily work becomes a whole number. B works every day, and A and C join him on every third day.
Work done in a day:
A: \(60\div10=6\) units, B: \(60\div12=5\) units, C: \(60\div15=4\) units
B alone (days 1 and 2 of every three): 5 units a day
A, B and C together (day 3): \(6+5+4=15\) units
Day by day:
Every 3 days: \(5+5+15=25\) units
After 6 days: \(2\times25=50\) units; 10 units are left
Day 7 (B alone): 55 units; day 8 (B alone): 60 units, and the work is finished
So the work is completed in 8 days.