Step-by-step explanation:
Let total number of girls and boys be x and y respectively.
[tex] \therefore \: \frac{3}{4} x = \frac{2}{5} y \\ \\ \therefore \: \frac{x}{y} = \frac{2}{5} \times \frac{4}{3} \\ \\ \therefore \: \frac{x}{y} = \frac{2 \times 4}{5 \times 3} \\ \\ \therefore \: \frac{x}{y} = \frac{8}{15} \\ \\ [/tex]
[tex] \therefore \: \frac{3}{4} x = \frac{2}{5} y \\ \\ \therefore \: \frac{x}{y} = \frac{2}{5} \times \frac{4}{3} \\ \\ \therefore \: \frac{x}{y} = \frac{2 \times 4}{5 \times 3} \\ \\ \therefore \: \frac{x}{y} = \frac{8}{15} \\ \\ \therefore \: \: \frac{8}{15} \: of \: the \: whole \: class \: have \: cell \: \\ phones.[/tex]