Solution:Information Given in the Question:
25% of efficiency of A / 25% of efficiency of (B + C) = 1/1
Efficiency of A = Efficiency of B + C
Time taken by (A + B) to complete 50% work : Time taken by C to complete whole work
= 1 : 4
A + B + C together can complete the work in 3 days
Concept/Formula Used in the Question:
Work = Efficiency × Time
Efficiency is inversely proportional to time (more efficient = less time):
If total work = W, then time to complete = W / efficiency
If A + B + C complete work in 3 days → Total work = (A + B + C)’s efficiency × 3
Detailed Explanation:
Let efficiency of A = a
Since A = B + C → Efficiency of B + C = a
So total efficiency (A + B + C) = a + (B + C) = a + a = 2a
Let total work = LCM of days = 6a units
So if efficiency = 2a, then time to complete = 6a / 2a = 3 days
Now, from second condition:
Time taken by A + B to do 50% of work : Time taken by C to do full work = 1 : 4
Let efficiency of A + B = a + b
Efficiency of C = c = a − b (since A = B + C → C = A − B)
Now,
Time taken by A + B to do 50% of work = (0.5 × 6a) / (a + b)
Time taken by C to do full work = (6a) / (a − b)
Given their ratio = 1 : 4
(3a)/(a + b) : (6a)/(a − b) = 1 : 4
(3a/(a + b)) × ((a − b)/6a) = 1/4
(3(a − b)) / (6(a + b)) = 1/4
( (a − b) / (2(a + b)) ) = 1/4
2(a − b) = a + b
2a − 2b = a + b
a = 3b
So, A’s efficiency = a = 3b
Then, B = b
So, C = a − b = 3b − b = 2b
Now, A + B + C = 3b + b + 2b = 6b
Total work = 6a = 6 × 3b = 18b
Time taken by B alone = Total work / B’s efficiency = 18b / b = 18 days