There are 420 girls and boys at a concert The ratio of girls to boys at the concert is 3 to 7 How many girls are at the concert?

3+7=10 (3 and 7 are both ratio numbers)

420/10=42 (10 is the sum of both ratio)

3x42=126 girls (3 is ratio of girls)

7x42=294 boys (7 is ratio of boys)