The problem in the image provides the following details:

• A school construction project is expected to be completed in 42 days with 60 workers.
• On the 21st day, 17 workers become sick and 3 workers have minor injuries, and they only return to work after 2 days.
• The goal is to find how many additional workers are needed to ensure the project finishes on time.

Solution Approach:

1. Initial Workload Calculation:

   • Total work = $60 \, \text{workers} \times 42 \, \text{days} = 2520 \, \text{worker-days}$
   • This means the project requires 2520 worker-days to be completed on time.

2. Work Done in the First 20 Days:

   • In the first 20 days, 60 workers work every day: $60 \, \text{workers} \times 20 \, \text{days} = 1200 \, \text{worker-days}$
   • So, after 20 days, 1200 worker-days have been completed, leaving: $2520 - 1200 = 1320 \, \text{worker-days remaining}$

3. Work on Day 21 and Day 22 (with reduced workers):

   • On the 21st and 22nd days, only $60 - 17 - 3 = 40 \, \text{workers}$ are working.
   • Work done in these 2 days: $40 \, \text{workers} \times 2 \, \text{days} = 80 \, \text{worker-days}$
   • After these two days, the remaining work is: $1320 - 80 = 1240 \, \text{worker-days remaining}$

4. Work After Day 23 (normal workers back):

   • From day 23, all 60 workers return.
   • Time remaining = $42 - 22 = 20 \, \text{days}$.
   • Work capacity with 60 workers for the remaining 20 days is: $60 \, \text{workers} \times 20 \, \text{days} = 1200 \, \text{worker-days}$
   • This is 40 worker-days short ($1240 - 1200 = 40$).

5. Finding the Additional Workers:

   • To cover the remaining 40 worker-days over 20 days, we need: $\frac{40 \, \text{worker-days}}{20 \, \text{days}} = 2 \, \text{workers}$
   • Therefore, 2 additional workers are needed.

Answer:

The minimal number of additional workers needed is 2.

Would you like more details or have any questions?

Here are 5 related questions:

1. How would the solution change if the 17 workers only returned after 3 days instead of 2?
2. What would happen if the workers’ productivity was not uniform?
3. How would the calculations change if only 50 workers were available from the start?
4. What if the 3 workers who were injured never returned? How many more workers would be needed?
5. Could overtime or longer working hours reduce the need for additional workers?

Tip: Breaking down complex problems into smaller time frames or stages can simplify your calculations!