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Three persons A, B, and C together have to finish a task. It takes 75 minutes  for them 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. What is the time taken by A alone to finish the task?
  • a)
    10 hours
  • b)
    15 hours
  • c)
    20 hours
  • d)
    30 hours
Correct answer is option 'D'. Can you explain this answer?
Verified Answer
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 - 4 b + 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) 
15b + 25 - 20b = 3b2 + 5b,  
3b2 + 10b - 25 = 0
.*.b = 5/3 o r -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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Most Upvoted Answer
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.

Let's assume that the total time taken by A, B, and C to finish the task is T minutes.

One-fourth of the task takes 75 minutes:
⇒ (1/4)T = 75
⇒ T = 75 * 4
⇒ T = 300 minutes

A and C together take 75% of the time taken by A and B together to finish the task:
⇒ (A + C) = 0.75 * (A + B)

Since C takes 300 minutes less than B to finish the task:
⇒ C = B - 300

Now, we can substitute the value of C in terms of B in the equation (A + C) = 0.75 * (A + B):

⇒ (A + B - 300) = 0.75 * (A + B)
⇒ 0.25 * (A + B) = 300
⇒ A + B = 300 / 0.25
⇒ A + B = 1200

Substituting the value of A + B = 1200 in the equation (A + C) = 0.75 * (A + B):

⇒ A + C = 0.75 * 1200
⇒ A + C = 900

As we know that T = 300 minutes and A + B = 1200, we can find out the value of A by subtracting the sum of B and C from the total time T:

⇒ A = T - (B + C)
⇒ A = 300 - (1200 - 900)
⇒ A = 300 - 300
⇒ A = 0

This means that A alone takes 0 minutes to finish the task, which is not possible.

Therefore, there must be an error in the given information or the question itself.
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Three persons A, B, and C together have to finish a task. It takes 75 minutes for them to finish one-fourth of the task. A and C together take 75% of thetime taken by A and B together to finish the task. C takes 300 minutes less than B to finish the task. What is the time taken by A alone to finish the task?a)10 hoursb)15 hoursc)20 hoursd)30 hoursCorrect answer is option 'D'. Can you explain this answer?
Question Description
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