90 students represent x percent of the boys at Jones Elementary School. If the boys at Jones Elementary make up 20% of the total school population of x students, what is x? Choose one.
A) 125	B) 150	C) 212	D) 250	E) 500

Rationale: 90 = x / 100 * 20 / 100 * x = > x ^ 2 = 9 * 10000 / 2 = > x = 212 c
Answer: C