The proportion is [tex]\frac{girls}{boys}[/tex] or [tex]\frac{10}{15}[/tex] = [tex]\frac{x}{21}[/tex] cross multiply to get 10*21 = 15x; simplify that to 210 = 15x then divide both sides by 15 to get 14 = x so no, there is not 16 girls in the class, there is 14