The ratio of girls to boys who participated in the quiz bowl was 7:5. There were 42 girls in the competition. How many boys participated?

girs: boys  = 7:5 42 : boys = 7: 5 42 : b = 7 : 5 42 / b  = 7 / 5  Cross multiply b*7  = 42 * 5 7b = 42* 5 b = 42*5/7 = 6*5 = 30 boys that participated are 30.