The 5*5 grid shown contains a collection of squares with sizes from 1*1 to 5*5. How many of these squares contain the black center square?
well let's take a look...
it's in the 5x5 square
it's in all 4 of the 4x4 squares
it's in all 9 of the 3x3 squares
It's in 4 of the 2x2 squares
It's in 1 of the 1x1 squares
for a total of 19 squares