You can rewrite this problem into an equation. You know that the ratio of boys to girls is 4 to 3, which is the same as:
[tex] \frac{boys}{girls} = \frac{4}{3}[/tex]
Cross multiply to get to 4G = 3B
Divide both sides by 4, to isolate the G (# of girls).
G = 3B / 4 = 0.75B
So you know that B + G = 35 (boys plus girls equals 35). Replace the G in this equation with the one you found above so that the entire equation only has one variable.
B + G = 35
B + 0.75B = 35
1.75B = 35
1.75B / 1.75 = 35 / 1.75
B = 20
However, you need to find G. So plug B back into one of the equations:
B + G = 35
20 + G = 35
G = 15
