If 15% of 30% of 50% of a number is 90, then what is the number? Options:
A) 4000 B) 3050 C) 4400 D) 4500 E) none of these

Rationale: "let the number be a given , 15 / 100 * 30 / 100 * 50 / 100 * a = 90 = > 3 / 20 * 3 / 10 * 1 / 2 * a = 90 = > a = 10 * 20 * 10 * 2 = 4000 . answer : a"
Answer: A