A man undertakes to do a work in 150 days. He employs 200 men. He finds that only a quarter of the work is done in 50 days. How many additional men should he employ so that the whole work is finished in time?
100
Solving Work and Time Problems: Finding Additional Men
This problem is about how the amount of work done relates to the number of men working and the time they spend. We are given a situation where a task needs to be completed within a specific timeframe, and we need to figure out how to adjust the workforce to meet the deadline after a certain amount of work has been done.
Understanding the Relationship
The core idea behind these types of problems is that the total "work effort" required to complete a task is constant. Work effort can be thought of as the product of the number of workers, the time they work, and their efficiency. Assuming efficiency remains constant, the total work effort is proportional to (Number of Men) \(\times\) (Number of Days).
If the work done is also considered, the relationship can be expressed as:
\[ \frac{M_1 \times D_1}{W_1} = \frac{M_2 \times D_2}{W_2} \] Where:
- \(M_1\) = Initial number of men
- \(D_1\) = Initial number of days
- \(W_1\) = Amount of work done in the initial phase
- \(M_2\) = Number of men required for the second phase
- \(D_2\) = Number of days for the second phase
- \(W_2\) = Amount of work to be done in the second phase
Applying the Formula to the Problem
Let's break down the information given in the problem:
- Total time allowed for the work = 150 days.
- Initial number of men employed = 200 men.
- Time spent in the first phase = 50 days.
- Work done in the first phase = A quarter of the total work, which is \( \frac{1}{4} \).
Now, let's determine the details for the second phase:
- Remaining time to complete the work = Total time - Time spent = 150 days - 50 days = 100 days.
- Remaining work to be done = Total work - Work done = \( 1 - \frac{1}{4} = \frac{3}{4} \).
- Let \(M_2\) be the total number of men required to complete the remaining work in the remaining time.
Using the formula \( \frac{M_1 \times D_1}{W_1} = \frac{M_2 \times D_2}{W_2} \), we can plug in the values:
\[ \frac{200 \times 50}{\frac{1}{4}} = \frac{M_2 \times 100}{\frac{3}{4}} \]
Let's solve for \(M_2\):
\[ \frac{200 \times 50}{\frac{1}{4}} = 200 \times 50 \times 4 = 40000 \]
\[ \frac{M_2 \times 100}{\frac{3}{4}} = M_2 \times 100 \times \frac{4}{3} = M_2 \times \frac{400}{3} \]
So, the equation becomes:
\[ 40000 = M_2 \times \frac{400}{3} \]
To find \(M_2\), we rearrange the equation:
\[ M_2 = 40000 \times \frac{3}{400} \]
\[ M_2 = \frac{40000 \times 3}{400} = \frac{100 \times 3 \times 400}{400} = 100 \times 3 \]
\[ M_2 = 300 \]
This means a total of 300 men are needed for the remaining 100 days to finish the work on time.
Calculating Additional Men
The question asks for the number of additional men required. The initial number of men was 200. The total number of men needed for the rest of the project is 300.
Additional men = Total men needed - Initial men
Additional men = 300 - 200 = 100 men.
Therefore, 100 additional men should be employed to ensure the whole work is finished within the original 150-day deadline.
Summary of Steps
- Identify the initial conditions (Men, Days, Work Done).
- Identify the target conditions (Remaining Days, Remaining Work).
- Use the man-days-work relationship formula: \( \frac{M_1 \times D_1}{W_1} = \frac{M_2 \times D_2}{W_2} \).
- Solve for the required number of men (\(M_2\)) for the second phase.
- Calculate the additional men needed by subtracting the initial number of men from \(M_2\).
| Phase | Men (M) | Days (D) | Work (W) |
|---|---|---|---|
| Phase 1 (Given) | 200 | 50 | \(\frac{1}{4}\) |
| Phase 2 (Required) | \(M_2\) (to find) | 100 | \(\frac{3}{4}\) |
Revision Table: Key Concepts in Work and Time
| Concept | Explanation | Formula/Relationship |
|---|---|---|
| Work Rate | Amount of work done per unit of time by one person/unit. | Work = Rate \(\times\) Time |
| Man-Days | A unit representing the amount of work one man can do in one day. Total work is often measured in man-days. | Total Work = Number of Men \(\times\) Number of Days (assuming constant rate) |
| Inverse Proportion | If the number of men increases, the time taken to complete the same amount of work decreases (assuming constant rate). | \( M_1 \times D_1 = M_2 \times D_2 \) (for same work W) |
| Direct Proportion | If the amount of work increases, the time taken or the number of men required increases (assuming other factors are constant). | \( \frac{W_1}{D_1} = \frac{W_2}{D_2} \) (for same men M) or \( \frac{W_1}{M_1} = \frac{W_2}{M_2} \) (for same days D) |
Additional Information: Work and Time Problem Variations
Work and time problems can come in various forms, including:
- Problems involving individual work rates and combined work rates of multiple people.
- Problems where efficiency varies between workers.
- Problems involving pipes and cisterns (where filling/emptying is the "work").
- Problems where some workers leave or join during the task.
The key to solving these problems is often to first determine the total amount of work (sometimes in "units" or "man-days") or the individual rates, and then calculate how much work is done or needs to be done under different conditions. The formula \( \frac{M_1 \times D_1}{W_1} = \frac{M_2 \times D_2}{W_2} \) is a powerful tool for problems involving changes in the number of workers and time for a given amount of work.
Similar Questions
A work when done by 10 women is completed in 12 days. The same work can be completed in 8 days by 5 men. How many days will it take to complete when 6 women and 3 men are employed to perform the same job?
30 men can complete a job in 40 days. However, after 24 days some men left the job. The remaining people took another 40 days to complete the job. The number of men who left the job is
Important Questions from Work and Wages
A can complete a work alone in 8 days. B can complete the same work alone in 12 days. C alone complete the same work in 16 days. They complete the work in 3 days with the help of D. If they get Rs.12000 for the work, then how much money does the D get?
If 15 men can complete a work in 16 days by working 8 hours daily, then in how many days will 10 men complete the work by working 12 hours daily?
10 men working 8 hours a day can finish a work in 28 days. In how many days, 8 men working 5 hours a day with complete 50% of that work?
A can do a work in 12 days and B in 16 days. They undertook to do it for Rs. 6000 with the help of ‘C’ they completed the work in 6 days. What is the share of A?
Twenty lamps can be lighted for 6 hr a day for 20 days at a cost of Rs. 100. How much would be the cost of lighting 40 lamps, 8 hr for 12 days?
