Squaring numbers in the 20s

1. Square the last digit (keep the carry)   _ _ X
2. Multiply the last digit by 4, add the carry   _ X _
3. The first digit will be 4 plus the carry:   X _ _

   Example:

     If the number to be squared is 24:

1. Square the last digit (keep the carry):
       4 x 4 = 16 (keep 1)     _ _ 6
2. Multiply the last digit by 4, add the carry:
       4 x 4 = 16, 16 + 1 = 17    _ 7 _
3. The first digit will be 4 plus the carry:
       4 (+ carry): 4 + 1 = 5    5 _ _
4. So 24 x 24 = 576.

   See the pattern?

     If the number to be squared is 26:

1. Square the last digit (keep the carry):
       6 x 6 = 36 (keep 3)    _ _ 6
2. Multiply the last digit by 4, add the carry:
       4 x 6 = 24, 24 + 3 = 27 (keep 2)   _ 7 _
3. The first digit will be 4 plus the carry:
       4 (+ carry): 4 + 2 = 6  6 _ _.
4. So 26 x 26 = 676.