Most People Don't Find Them All
Number Theory
Level
1
How many rectangles (including squares) are in a 10 by 10 square?
55
3015
3020
3025
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1 solution
It might sound complicated (or very easy), but the solution is to calculate the lines on the sides. There are 10 + 9 + 8 ... +1 which equals 55. And that means the other side is also 55. And like area, 55 times 55 equals 3025, which is the answer.