Tutorial 28
Squaring a 2-digit number beginning with 1

  1. Take a 2-digit number beginning with 1.
  2. Square the second digit
    (keep the carry)   _ _ X
  3. Multiply the second digit by 2 and
    add the carry (keep the carry)   _ X _
  4. The first digit is one
    (plus the carry)   X _ _

   Example:

  1. If the number is 16, square the second digit:
    6 × 6 = 36   _ _ 6
  2. Multiply the second digit by 2 and
    add the carry: 2 × 6 + 3 = 15   _ 5 _
  3. The first digit is one plus the carry:
    1 + 1 = 2   2 _ _
  4. So 16 × 16 = 256.

   See the pattern?

  1. For 19 × 19, square the second digit:
    9 × 9 = 81   _ _ 1
  2. Multiply the second digit by 2 and
    add the carry: 2 × 9 + 8 = 26   _ 6 _
  3. The first digit is one plus the carry:
    1 + 2 = 3   3 _ _
  4. So 19 × 19 = 361.