Bunuel
The ratio of boys to girls in the junior class is 2 to 3 respectively and the ratio of girls to boys in the senior class is 7 to 3 respectively. If there are 300 more students in the senior class than in the junior class and the combined ratio of boys to girls in both classes is 8 to 17 respectively, how many students are in the senior class?
(A) 100
(B) 300
(C) 375
(D) 400
(E) 500
We can use weighted averages here the way we use in mixtures.
Concentration of boys in junior class =\( \frac{2}{5} = \frac{20}{50}\)
Concentration of boys in senior class = \(\frac{3}{10} = \frac{15}{50}\)
Overall concentration of boys = \(\frac{8}{25} = \frac{16}{50}\)
\(\frac{Ws}{Wj} = \frac{(20 - 16)}{(16 - 15)} = \frac{4}{1}\)
Students in senior class : Students in junior class = 4 : 1
The difference of 3 in ratio terms is 300 so multiplier is 100.
Number of students in senior class = 4 * 100 = 400
Answer (D