A, B and C can do a piece of work in 20, 30 and 60 days respectively. ...
Given information:
A, B, and C can complete a piece of work in 20, 30, and 60 days respectively.
Approach:
To find the number of days A takes to complete the work with the assistance of B and C on every third day, we need to calculate the combined work done by A, B, and C in a single day.
Let's assume that the total work is 60 units (LCM of 20, 30, and 60).
Calculation:
A's work efficiency = 60/20 = 3 units/day
B's work efficiency = 60/30 = 2 units/day
C's work efficiency = 60/60 = 1 unit/day
Work done on every third day:
On every third day, A works alone and completes 3 units of work.
Work done on the remaining days:
On the remaining two days, A, B, and C work together.
Their combined work efficiency = A's efficiency + B's efficiency + C's efficiency = 3 + 2 + 1 = 6 units/day
Work done in 2 days:
On the two days when A, B, and C work together, they complete 6 units of work.
Work done in 20 days:
In 20 days, A will work alone on every third day and complete 3 units of work. On the remaining 19 days, A, B, and C will work together and complete 19 * 6 = 114 units of work.
Total work done:
In 20 days, A will complete 3 + 114 = 117 units of work.
Number of days A takes to complete the work:
Since the total work is 60 units, and A completes 117 units of work in 20 days, the number of days A takes to complete the work is (20 * 60) / 117 = 10.25 days.
Since the number of days cannot be in decimals, we round it up to the nearest whole number, which is 11.
Therefore, A can complete the work if he is assisted by B and C on every third day in 11 days.
Final Answer: Option (12 days)