Hi minuit7,

This question can be solved with a bit of Arithmetic and 'bunching.'

We're told that the first two rows of parking spaces contain 20 and 21 spaces respective, then the following 15 rows increase by 2 each (re: 23, 25, 27, etc.). We're asked for the TOTAL number of parking spaces.

The first two rows total 20+21 = 41 spaces. The remaining 15 rows are the odd numbers from 23 through 51, inclusive. By adding the smallest and largest of those numbers, we get:

23 + 51 = 74

By adding the next smallest and next biggest, we get:

25 + 49 = 74

This pattern is consistent, so we'll end up with 7 "pairs" of numbers that add up to 74 and one number "in the middle" that doesn't 'pair up': 37.

Thus, the total number of spaces is... 41 + 7(74) + 37 = 596

Final Answer: C

GMAT assassins aren't born, they're made,
Rich