Final answer:
The ratio of the number of children who can swim to the number of children who cannot swim at the summer camp is 2:1.
Step-by-step explanation:
The ratio of the number of children who can swim to the number of children who cannot swim can be found by dividing the number of children who can swim by the number of children who cannot swim.
According to the given information, there are 23 boys and 17 girls who can swim, and there are 9 boys and 11 girls who cannot swim.
The total number of children who can swim is 23 + 17 = 40, and the total number of children who cannot swim is 9 + 11 = 20.
Therefore, the ratio of the number of children who can swim to the number of children who cannot swim is 40:20, which simplifies to 2:1.