
 Take a 2digit number
ending in 3.
 The last digit will be _ _
_ 9.
 Multiply the first digit
by 6: the 2nd number will be
the next to the last digit: _ _ X 9.
 Square the first digit and
add the number carried from
the previous step: X X _ _.
Example:
 If the number is 43,
the last digit is _ _ _ 9.
 6 × 4 = 24 (six times the
first digit): _ _ 4 9.
 4 × 4 = 16 (square the
first digit), 16 + 2 = 18
(add carry): 1 8 4 9.
 So 43 × 43 = 1849.
See the pattern?
 For 83 × 83, the last
digit is _ _ _ 9.
 6 × 8 = 48 (six times the
first digit): _ _ 8 9.
 8 × 8 = 64 (square the
first digit), 64 + 4 = 68
(add carry): 6 8 8 9.
 So 83 × 83 = 6889.

