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Question

X can do a piece of work in 4 days and Y can do the same piece of work in 6 days. Which of the following statements is/are correct ?
I. If X and Y work alternately starting with X, then the piece of work will be finished on the fifth day.
II. If X and Y work alternately starting with Y, then the piece of work will be finished in less than 5 days.
Select the answer using the code given below :

This question was previously asked in
CDS 2 2026 Maths Question Paper (13-Sep-2026)
The correct answer is

I only

To solve this question, we need to evaluate each statement based on the given conditions. Let's assess each statement step-by-step:

Given:

  • X can finish the work in 4 days.
  • Y can finish the same work in 6 days.

Calculations:

  • Work done by X in 1 day \(= \frac{1}{4}\).
  • Work done by Y in 1 day \(= \frac{1}{6}\).

Let's calculate the work done when they work alternately:

  1. Statement I: If X and Y work alternately starting with X, then the piece of work will be finished on the fifth day.
    • Days 1 and 2: Combination of 1 day of work by X and 1 day of work by Y.
      Work done in 2 days \(= \frac{1}{4} + \frac{1}{6} = \frac{3}{12} + \frac{2}{12} = \frac{5}{12}\).
    • Days 3 and 4: Another combination of 1 day of work by X and 1 day of work by Y repeat.
      Additional work done \(= \frac{5}{12}\).
  • Additional work done by X on the 5th day \(= \frac{1}{4}\).
  • \(= \frac{5}{6} + \frac{1}{4} = \frac{10}{12} + \frac{3}{12} = 1\).
  1. Statement II: If X and Y work alternately starting with Y, then the piece of work will be finished in less than 5 days.
    • Days 1 and 2: 1 day of work by Y, followed by 1 day of work by X.
      Work done in 2 days \(= \frac{1}{6} + \frac{1}{4} = \frac{2}{12} + \frac{3}{12} = \frac{5}{12}\).
    • Days 3 and 4: The same pattern repeats.
      Additional work done \(= \frac{5}{12}\).
  • Additional work done by Y on the 5th day \(= \frac{1}{6}\).
  • \(= \frac{5}{6} + \frac{1}{6} = 1\).

Final Conclusion: The correct answer is "

I only

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