How to Work with Ratios and Proportions - dummies 208. To begin, set up a proportion based on the ratio of girls to boys: Now, you want to increase the terms of the fraction 7/9 so that the number representing boys becomes 117. (To do this, notice that 117 / 9 = 13, so 9 / 13 = 117): Therefore, the camp has 91 girls and 117 boys, so the total number of children is 208. $825,000.