Three persons A, B, and C together have to finish a task. It takes 75 ...
Since A, B and C take 75 minutes to finish one-fourth of a task, they take 300 minutes i.e. 5 hours, to complete the entire task.
Let the total work be some multiple of 5, say 25 units.
Let a, b and c be the amount of work done by A, B and C per hour.
a + b + c = 25/5 = 5 units/hour ... (i)
A and C together take 75% of the time taken by A and B together to finish the task.

Substituting this value of a in (i),
3c-4b + b + c = 5

4c —3b = 5 ... (ii)
C takes 300 minutes less than B to finish the task i.e. C takes 5 hours less
Substituting the value of c from (ii) in (iii)

156 + 25 - 206 = 36
2 + 56

36
2+ 106-25 = 0

6 = 5/3 or-15
b has to be positive as it corresponds to amount of work done by B per hour i.e. b = 5/3
Substituting this value in (iii), c = 5/2
Substituting the value of b and c in (i),
Hence, option 4.
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Three persons A, B, and C together have to finish a task. It takes 75 ...
Given:
- A, B, and C together take 75 minutes to finish one-fourth of the task.
- A and C together take 75% of the time taken by A and B together to finish the task.
- C takes 300 minutes less than B to finish the task.
To find:
The time taken by A alone to finish the task.
Let's solve this step by step:
Step 1: Time taken by A, B, and C to finish one-fourth of the task
Let's assume the total time taken by A, B, and C to finish the task is T minutes.
So, the time taken by A, B, and C to finish one-fourth of the task is T/4 minutes.
Given that A, B, and C together take 75 minutes to finish one-fourth of the task, we can write the equation as:
T/4 = 75
Step 2: Time taken by A and B to finish the task
Let's assume the time taken by A and B together to finish the task is X minutes.
So, the time taken by A and C together to finish the task would be 0.75X minutes (75% of X).
Step 3: Time taken by C to finish the task
Given that C takes 300 minutes less than B to finish the task, we can write the equation as:
X - 300 = C
Step 4: Expressing the time taken by A, B, and C to finish the task in terms of X
Since A and C together take 0.75X minutes to finish the task, and C takes X - 300 minutes, we can write the equation as:
0.75X + X - 300 = T
Step 5: Solving the equations
Now, we have two equations:
T/4 = 75
0.75X + X - 300 = T
Let's solve these equations simultaneously.
From the first equation, we can find the value of T:
T = 4 * 75 = 300
Substituting the value of T in the second equation:
0.75X + X - 300 = 300
1.75X = 600
X = 600 / 1.75
X ≈ 342.86
Step 6: Finding the time taken by A alone to finish the task
Since A and B together take X minutes to finish the task, and B takes X - 300 minutes, we can write the equation as:
X = A + X - 300
A = 300
Therefore, the time taken by A alone to finish the task is 300 minutes, which is equivalent to 5 hours or 5 * 60 = 300 minutes.
Hence, the correct answer is option D) 30 hours.