A and B can do a piece of work in 18 days. B and C together can do it in 30 days. If A is twice as good a workman as C, find in how many days B alone can do the work?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. 90 days.
A + B can complete work in 18 days.
B + C can complete work in 30 days.
The efficiency of A: C = 2: 1.
Let the efficiency of A = 2x units/day and C = x unit/day.
Total work = LCM of 18 and 30 = 90 units.
A + B = 90/18 = 5
2x + B = 5
B = 5 - 2x........(1)
C + B = 90/30 = 3
x + B = 3
B = 3 - x..........(2)
3 - x = 5 - 2x
x = 2
Efficiency of B = 3 - 2 = 1 unit/day.
Time taken by B to complete the work = 90/1 = 90 days.