The problem states:

• Mr. Lou teaches 7 reading groups.
• Each group has 5 students.
• If 3 students are absent, how many students does Mr. Lou teach today?

To find the solution, we need to calculate the total number of students Mr. Lou would teach without any absences and then subtract the absent students.

1. Calculate the total number of students in all groups: $7 \text{ groups} \times 5 \text{ students per group} = 35 \text{ students}$

2. Subtract the 3 absent students: $35 - 3 = 32$

The correct mathematical expression representing this situation is: $7 \times 5 - 3$ This corresponds to the bottom-right choice in the image.

Would you like more details or have any other questions?

Here are some related questions:

1. What if 2 more students are absent? How would the expression change?
2. How can we generalize this problem for any number of absent students?
3. How do you distribute multiplication over subtraction in expressions?
4. Can we use parentheses to change the result in any of the other given expressions?
5. How would the problem change if the number of groups varied instead of the number of absences?

Tip: Always evaluate expressions inside parentheses first, as they change the order of operations and the result of the calculations.