Given averages: Boys = 52, Girls = 42, Combined = 50.

Let the proportion of boys be \(p\) (so girls = \(1-p\)). Weighted mean gives: $$52p + 42(1-p) = 50$$ $$52p + 42 - 42p = 50 \Rightarrow 10p = 8 \Rightarrow p = 0.8.$$

Percentage of boys \(= 0.8 \times 100\% = \boxed{80\%}\).