120 students represent x percent of the boys at a school. If the boys at the school make up 30% of the total school population of x students, what is x?  Pick.
A) 120  B) 150  C) 180  D) 200  E) 250

Rationale: "let b be the number of boys in the school . 120 = xb / 100 b = 0.3 x 12000 = 0.3 x ^ 2 x ^ 2 = 40000 x = 200 the answer is d ."
Answer: D