Answer:
ratio of boys to girls= 4:7
number of girls=21
now,
[tex] \frac{boys}{girls} \times \frac{no.of \: boys}{no.of \: girs} [/tex]
[tex] \frac{4}{7} \times \frac{boys}{21} [/tex]
[tex]4 \times 21 = 7boys\: \\ \: ({cross multiplication})[/tex]
[tex]84 = 7boys[/tex]
[tex] \frac{84}{7 \: } = boys \: \: \: (dividing \: 84 \: by \: 7)[/tex]
[tex]12 = boys[/tex]
[tex]no.of \: boys = 12[/tex]
