Answer: he sold 9 pairs of dress shoes.
he sold 4 pairs of athletic shoes.
Explanation:
Let x represent the number of pairs of dress shoes that he sells.
Let y represent the number of pairs of athletic shoes that he sells.
The total number of pairs of shoes that he sold in a day is 13. It means that
x + y = 13
The salesman receives a commission of $4 for every pair of dress shoes he sells. He is paid $3 for every pair of athletic shoes he sells. The commission that he got on that day was $48. It means that
4x + 3y = 48- - - - - - - - - - 1
Substituting x = 13 - y into equation 1, it becomes
4(13 - y) + 3y = 48
52 - 4y + 3y = 48
- 4y + 3y = 48 - 52
- y = - 4
y = 4
x = 13 - y = 13 - 4
x = 9