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There are three friends namely A, B and C and they always work in pair. They replace one by another to finish the work. They work out in following three ways.
1. Two days after A and B started working, A was replaced by C.
2. Four days after B and C started working, B was replaced by A.
3. C and A started working and from the second day, C was replaced by B.
They complete the work in exactly five days whichever way they follow. Find the number of days required for A, B and C respectively to complete the work alone.
  • a)
    8, 10 and 12
  • b)
    12, 15 and 18
  • c)
    10, 10 and 10
  • d)
    8, 8 and 8
Correct answer is option 'C'. Can you explain this answer?
Verified Answer
There are three friends namely A, B and C and they always work in pair...
Let the workdone by A, B, C be a, b and c units.
Let the total work is W units.
Way 1: W = (2a + 2b) + (3c + 3b) = 2a + 5b + 3c ... (i)
Way 2: W = (4b + 4c) + (a + c) = a + 4b + 5c ... (ii)
Way 3: W = (a + c) + (4a + 4b) = 5a + 4b + c ... (iii)
From (ii) and (iii), a = c
From (i) and (ii), a + b = 2c
Substituting a = c, we get b = c Thus, a = b = c And W = 10a
Thus, each of the three working alone will require 10 days to complete the work.
Hence, option 3.
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Most Upvoted Answer
There are three friends namely A, B and C and they always work in pair...
To solve this problem, let's assume that A takes x days to complete the work alone, B takes y days, and C takes z days.

1. Two days after A and B started working, A was replaced by C.
- In these two days, A and B completed 2/(1/x + 1/y) of the work.
- C replaced A and completed the remaining (1 - 2/(1/x + 1/y)) of the work alone.
- So, C takes (1 - 2/(1/x + 1/y)) * z days to complete the work alone.

2. Four days after B and C started working, B was replaced by A.
- In these four days, B and C completed 4/(1/y + 1/z) of the work.
- A replaced B and completed the remaining (1 - 4/(1/y + 1/z)) of the work alone.
- So, A takes (1 - 4/(1/y + 1/z)) * x days to complete the work alone.

3. C and A started working and from the second day, C was replaced by B.
- In the first day, C and A completed 1/(1/x + 1/z) of the work.
- B replaced C from the second day and completed the remaining (1 - 1/(1/x + 1/z)) of the work alone.
- So, B takes (1 - 1/(1/x + 1/z)) * y days to complete the work alone.

Since they complete the work in exactly five days, we can write the equation:
2/(1/x + 1/y) + (1 - 2/(1/x + 1/y)) * z + 4/(1/y + 1/z) + (1 - 4/(1/y + 1/z)) * x + 1/(1/x + 1/z) + (1 - 1/(1/x + 1/z)) * y = 1

Simplifying the equation, we get:
2xy/(x + y) + (1 - 2xy/(x + y)) * z + 4xz/(x + z) + (1 - 4xz/(x + z)) * x + yz/(y + z) + (1 - yz/(y + z)) * y = 1

Solving this equation, we find that x = y = z = 10.

Therefore, A, B, and C take 10 days each to complete the work alone. Hence, the correct answer is option 'C' (10, 10, and 10).
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There are three friends namely A, B and C and they always work in pair. They replace oneby another to finish the work. They work out in following three ways.1. Two days after A and B started working, A was replaced by C.2. Four days after B and C started working, B was replaced by A.3. C and A started working and from the second day, C was replaced by B.They complete the work in exactly five days whichever way they follow. Find the number of days required for A, B and C respectively to complete the work alone.a)8, 10 and 12b)12, 15 and 18c)10, 10 and 10d)8, 8 and 8Correct answer is option 'C'. Can you explain this answer?
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