First add the ratios together ( 3+5) this will give you 8. Then divide the total number of students by 8, this will get you 7. Now multiply 7 to 3 and multiply 7 to 5. As the ratio of boy to girl is 3 to 5, to find how many girls are in the school play we multiply 7 to 5. This makes 35 girls.
If you want to check, 7 x 3 =21 boys and 7 x 5=35 girls. 35 +21= 56 (the total number of students).
