At Mathville Junior High School, 30 boys and 20 girls wrote the Pascal Contest. Certificates were awarded to $30 \%$ of the boys and $40 \%$ of the girls. What percentage of all of the participating students received certificates?
(A) 34
(B) 35
(C) 36
(D) 17
(E) 70
In total, $30+20=50$ students wrote the Pascal Contest at Mathville Junior High.

Since $30 \%$ (or $\frac{3}{10}$ ) of the boys won certificates and $40 \%$ (or $\frac{4}{10}$ ) of the girls won certificates, then the total number of certificates awarded was $\frac{3}{10}(30)+\frac{4}{10}(20)=9+8=17$.

Therefore, 17 of 50 participating students won certificates. In other words, $\frac{17}{50} \times 100 \%=34 \%$ of the participating students won certificates.

ANSWER: (A)