In a certain boys camp, 20% of the total boys are from school A and 30% of those study science. If there are 21 boys in the camp that are from school A but do not study science then what is the total number of boys in the camp?	Answers:
A) 70  B) 245  C) 150  D) 35  E) 350

Rationale: "since 30 % of the boys from school a study science , then 70 % of the boys from school a do not study science and since 20 % of the total number of boys are from school a , then 0.2 * 0.7 = 0.14 , or 14 % of the boys in the camp are from school a and do not study science . we are told that this number equals to 21 , so 0.14 * { total } = 21 - - > { total } = 150 . answer : c ."
Answer: C