The sum of number of boys and girls in a school is 400. If the number of boys is x, then the number of girls becomes x% of the total number of students. The number of boys is?  Select the correct option.
A) 50  B) 40  C) 60  D) 80  E) 70

Rationale: "we have x + x % of 400 = 400 x + x / 100 * 400 = 400 5 * x = 400 x = 80 answer is d"
Answer: D