The rectangle below is covered with unit squares. Some of the squares are gray.
How many square units are NOT gray?
- 7
- 13 (correct answer)
- 20
- 27
Explanation: The whole rectangle is 5 squares across and 4 squares up, so it covers 20 square units. Counting the gray squares gives 7. That leaves 20 - 7 = 13 square units that are not gray. Choice A is the number of gray squares, choice C is the area of the whole rectangle, and choice D adds the two counts instead of subtracting.