The notation [x] means to take the greatest integer that is less than or equal to x. For example, [4.9] is 4, and is 5. The problem asks for the smallest positive integer n that makes the equation [n/4] - [n/9] = 2 true.
The fastest way to solve this is to test the answer choices, starting with the smallest, since we are looking for the minimum value.
Try n = 7:
[7/4] - [7/9] = [1.75] - [0.77] = 1 - 0 = 1. This is not 2.
Try n = 8:
[8/4] - [8/9] = - [0.88] = 2 - 0 = 2. This matches the equation.
Since we started with the smallest choice and found the answer, 8 is the minimum possible value of n.
Thus, the correct answer is B. 8.
Bunuel
Let [x] represent the greatest integer less than or equal to x. If n is a positive integer such that [n/4] - [n/9] = 2, what is the minimum possible value of n?
A. 7
B. 8
C. 9
D. 12
E. 19