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Question

A can lay railway track between two given stations in 22 days and B can do the same job in 10 days. With the help of C, they did the job in 2 days only. Then, C alone can do the job in

This question was previously asked in
RRB NTPC 2024 CBT 1 Question Paper (28-Aug-2025) (Shift 3)
The correct answer is
$2 \frac{32}{39} \text{ days}$

Understanding Work Rates

This problem involves calculating the time taken by an individual (C) to complete a job, given the times taken by others (A and B) individually and the time taken by all three together.

  • The rate of work is the reciprocal of the time taken to complete the job.
  • Rate = $\frac{1}{\text{Time}}$

Calculating Individual Work Rates

First, determine the work rate of A and B:

  • A's time = 22 days. A's rate = $\frac{1}{22}$ of the job per day.
  • B's time = 10 days. B's rate = $\frac{1}{10}$ of the job per day.

Calculating Combined Work Rate (A, B, and C)

The combined time for A, B, and C to complete the job is 2 days. Their combined work rate is:

  • Combined rate (A+B+C) = $\frac{1}{2}$ of the job per day.

Finding C's Work Rate

The combined rate is the sum of individual rates: Rate(A+B+C) = Rate(A) + Rate(B) + Rate(C). We can find C's rate by subtracting A's and B's rates from the combined rate.

  1. Calculate the combined rate of A and B: Rate(A) + Rate(B) = $\frac{1}{22} + \frac{1}{10}$
  2. Find a common denominator (LCM of 22 and 10 is 110): $\frac{5}{110} + \frac{11}{110} = \frac{16}{110} = \frac{8}{55}$ job per day.
  3. Calculate C's rate: Rate(C) = Rate(A+B+C) - (Rate(A) + Rate(B)) Rate(C) = $\frac{1}{2} - \frac{8}{55}$
  4. Find a common denominator (LCM of 2 and 55 is 110): Rate(C) = $\frac{55}{110} - \frac{16}{110} = \frac{39}{110}$ job per day.

Calculating C's Time to Complete the Job

C's time is the reciprocal of C's work rate.

  • C's time = $\frac{1}{\text{Rate(C)}} = \frac{1}{\frac{39}{110}}$ days
  • C's time = $\frac{110}{39}$ days

Converting to Mixed Fraction

To express $\frac{110}{39}$ as a mixed fraction:

  • Divide 110 by 39: $110 \div 39 = 2$ with a remainder of $32$ ($110 = 2 \times 39 + 32$).
  • Therefore, C's time = $2 \frac{32}{39}$ days.
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Similar Questions

  1. Anjani can do a certain piece of work in 24 days. Anjani and Khushbu can together do the same work in 12 days, and Anjani, Khushbu and Sushmita can do the same work together in 9 days. In how many days can Anjani and Sushmita do the same work together?
  2. Hema can do a certain piece of work in 30 days. Hema and Raji can together do the same work in 22 days, and Hema, Raji and Smitha can do the same work together in 15 days. In how many days can Hema and Smitha do the same work together?
  3. A can lay railway track between two given stations in 21 days and B can do the same job in 16 days. With the help of C, they did the job in 2 days only. Then, C alone can do the job in
  4. Working $5\text{ h}$ a day, A can complete a task in $8\text{ days}$ and working $6\text{ h}$ a day, B can complete the same task in $10\text{ days}$. Working $8\text{ h}$ a day, they can jointly complete the task in:
  5. A does half as much work as B in three-fourth of the time taken by B. If together they take $12\text{ days}$ to complete the work, how much time shall B take to do it alone?
  6. A is only $40\%$ as efficient as B. C is $50\%$ as efficient as A and B together. If C alone completes the task in $30\text{ days}$, then A, B and C together can complete the task in:
  7. A can complete a piece of work in 60 days. He worked for 15 days and B finished the remaining work in 30 days. If they work together then the work will be completed in:
  8. If 24 persons can complete a task in 5 days, in how many days, 6 persons would be able to complete it?
  9. 15 men or 25 women can reap a field in 22 days. How many days will 9 men and 18 women take to reap it?
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Important Questions from Time and Work

  1. A and B can do a piece of work in 18 days. B and C together can do it in 30 days. If A is twice as good a workman as C, find in how many days B alone can do the work?

  2. Two men and 7 women can complete a work in 28 days, whereas 6 men and 16 women can do the same work in 11 days. In how many days will 5 men and 4 women, working together, complete the same work?

  3. A man and a woman, working together can do a work in 66 days. The ratio of their working efficiencies is 3 ∶ 2. In how many days 6 men and 2 women together can do the same work?

  4. Each one of five men independently can complete a work in 20 days. The work is started by one person. Next day one more person joins and every next day one more person joins. From the fifth day, five persons continued working as a team. In how many days, will the work be completed?

  5. Numan does half the work as Gagan in 4/5 of the time. If together they take 16 days to complete a piece of work, then how long will it take Gagan to complete the work?

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