Question

the ratio of boys to girls at the movie is 4:7. If there are 21 girls, how many boys are at the movie?

Answer 1

`7x=21\\ x=3\\\\ 4x=4\cdot3=\boxed{12}`

Answer 2

`boys:girls=4:7\\\\girls=21\\\\therefore\\\\boys:21=4:7\\\\(boys)/(21)=(4)/(7)\ \ \ \ \ |cross\ myltiply\\\\7\ boys=4*21\\\\7boys=84\ \ \ \ \ |divide\ both\ sides\ by\ 7\\\\boys=84:7\\\\\boxed{boys=12}`