5 persons working 7 hours a day can create a list in 8 days. To do this work in 4 days 2 more men are involved how many hours they will have to work per day?

Options

A. 10 hours
B. 9 hours
C. 12 hours
D. 8 hours

Explanation

To solve the problem, we need to determine how many hours per day the 7 men will have to work to complete the same amount of work in 4 days.

### Step-by-Step Solution:

1. **Calculate the Total Work Done by the First Group:**
- The first group consists of 5 persons working 7 hours a day for 8 days.
- Total work done (in person-hours) = Number of persons × Hours per day × Number of days
\[ \text{Total Work} = 5 \text{ persons} \times 7 \text{ hours/day} \times 8 \text{ days} = 280 \text{ person-hours} \]

2. **Determine the New Group Size:**
- Now, 2 more men are added to the original 5 men, making a total of:
\[ 5 + 2 = 7 \text{ persons} \]

3. **Set Up the Equation for the New Group:**
- We need to find out how many hours (h) they need to work per day to complete the same amount of work (280 person-hours) in 4 days.
- The equation for the new group is:
\[ \text{Total Work} = \text{Number of persons} \times \text{Hours per day} \times \text{Number of days} \]
\[ 280 = 7 \text{ persons} \times h \text{ hours/day} \times 4 \text{ days} \]

4. **Simplify the Equation:**
- Rearranging the equation gives:
\[ 280 = 28h \]
- Divide both sides by 28 to solve for h:
\[ h = \frac{280}{28} = 10 \text{ hours} \]

### Final Answer:
The 7 persons will have to work **10 hours per day** to complete the work in 4 days.

---