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Question

12 men working 8 hours a day can completely build a wall of length 100 m, breadth 20 cm and height 5 m in 10 days. How many days will 16 men working 10 hours a day require to build a wall of length 200 m, breadth 60 cm and height 5 m ?

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

36

To solve this problem, we can use the concept of man-hours, a common technique in work and time problems. This approach calculates the total hours required to complete a job based on the number of workers and hours worked per day.

First, determine the volume of the wall that 12 men can build.

  1. Volume of original wall = Length × Breadth × Height 
    \(= 100 \, \text{m} \times 0.2 \, \text{m} \times 5 \, \text{m} = 100 \times 0.2 \times 5 = 100 \, \text{m}^3\)

Next, find out the total man-hours required to build the wall, given the current team configuration:

  1. Total man-hours = (Number of workers) × (Hours per day) × (Days) 
    \(= 12 \times 8 \times 10 = 960 \, \text{man-hours}\)

To build this wall, 960 man-hours are required. Now, calculate the volume of the new wall:

  1. Volume of new wall = Length × Breadth × Height 
    \(= 200 \, \text{m} \times 0.6 \, \text{m} \times 5 \, \text{m} = 600 \, \text{m}^3\)

The ratio of volumes gives us the ratio of man-hours needed:

  1. Volume Ratio = \(\frac{600}{100} = 6\)

Thus, the man-hours required for the new wall is:

  1. Total man-hours for new wall = 960 × 6 = 5760 man-hours

Now calculate how many days 16 men working 10 hours a day will take to complete this:

  1. Work done per day by 16 men = (Number of workers) × (Hours per day) 
    Work done per day = \(16 \times 10 = 160 \, \text{man-hours}\)
  2. Days required = \(\frac{5760}{160} = 36 \, \text{days}\)

Thus, the correct answer is: 36 days.

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Important Questions from Time and work

  1. A person can complete 20% of work in 8 days and another person y can complete 25% of the same work in 6 days. If they work together, in how many days will 40% of the work be completed?

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  5. Ram and Shyam work on a job together for four days and complete 60% of it. Ram takes leave then and Shyam works for eight more days to complete the job. How long would Ram take to complete the entire job alone?

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