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Question

Three workers, X, Y, and Z, can complete a certain job in 10 days, 12 days, and 15 days, respectively. Determine the number of days required for them to complete the job when they work together.

This question was previously asked in
RRB NTPC 2025 Graduate Level CBT 1 Question Paper (25-Mar-2026) (Shift 3)
The correct answer is

4 days

To determine the number of days required for workers X, Y, and Z to complete the job together, we use the concept of work and time, specifically the formula for combined work rate.

Step 1: Determine the work rate of each worker.

  • Worker X can complete the job in 10 days, so X's work rate is \(\frac{1}{10}\) of the job per day.
  • Worker Y can complete the job in 12 days, so Y's work rate is \(\frac{1}{12}\) of the job per day.
  • Worker Z can complete the job in 15 days, so Z's work rate is \(\frac{1}{15}\) of the job per day.

Step 2: Calculate the combined work rate.

The combined work rate when all workers work together is the sum of their individual work rates:

\(\frac{1}{10} + \frac{1}{12} + \frac{1}{15}\)

To add these fractions, we need a common denominator. The least common multiple of 10, 12, and 15 is 60.

Convert each work rate to have a denominator of 60:

  • \(\frac{1}{10} = \frac{6}{60}\)
  • \(\frac{1}{12} = \frac{5}{60}\)
  • \(\frac{1}{15} = \frac{4}{60}\)

Add these together:

\(\frac{6}{60} + \frac{5}{60} + \frac{4}{60} = \frac{15}{60} = \frac{1}{4}\)

Step 3: Calculate the time to complete the job together.

Since their combined work rate is \(\frac{1}{4}\), they can complete \(\frac{1}{4}\) of the job in one day. Therefore, they will complete 1 whole job in:

\(4 \text{ days}\)

Thus, the correct answer is 4 days.

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