Math Tricks

Squaring a 2-digit number ending in 8

1. Choose a 2-digit number ending in 8.
2. The last digit of the answer is always 4: _ _ _ 4
3. Multiply the first digit by 6 and add 6 (keep the
   carry): _ _ X _
4. Multiply the first digit by the next consecutive
   number and add the carry: the product is the first
   two digits: XX _ _.

Example:

1. If the number is 78:
2. The last digit of the answer is 4: _ _ _ 4
3. Multiply the first digit (7) by 6 and add 6 (keep the
   carry): 7 x 6 = 42, 42 + 6 = 48; the next digit of the
   answer is 8 (keep carry 4): _ _ 8 4
4. Multiply the first digit (7) by the next number (8)
   and add the carry (4):
   7 x 8 = 56, 56 + 4 = 60 (the first two digits): 6 0 _ _
5. So 78 x 78 = 6084.

See the pattern?

1. For 38 x 38
2. The last digit of the answer is 4: _ _ _ 4
3. Multiply the first digit (3) by 6 and add 6 (keep the
   carry): 3 x 6 = 18, 18 + 6 = 24; the next digit of the
   answer is 4 (keep carry 2): _ _ 4 4
4. Multiply the first digit (3) by the next number (4)
   and add the carry (2):
   3 x 4 = 12, 12 + 2 = 14 (the first two digits): 1 4 _ _
5. So 38 x 38 = 1444