Multiplying a 2-digit number by 77

1. Select a 2-digit number.
2. Multiply it by 7.
3. Add the digits from right to left
   (see examples, below).

   Example:

1. The 2-digit number chosen to multiply by 77 is 42.
2. Multiply by 7: 7 x 42 = 280 + 14 = 294
3. The last digit is the same: _ _ _ 4
4. Add right to left. 4 + 9 = 13: _ _ 3 _
   9 + 2 + 1(carry) = 12: _ 2 _ _
   First digit + carry: 2 + 1 = 3: 3 _ _ _
5. So 77 x 42 = 3234.

   See the pattern?

1. If the number to be multiplied by 77 is 84:
2. Multiply by 7: 7 x 84 = 560 + 28 = 588
3. The last digit is the same: _ _ _ 8
4. Add right to left. 8 + 8 = 16: _ _ 6 _
   8 + 5 + 1(carry) = 14: _ 4 _ _
   First digit + carry: 5 + 1 = 6: 6 _ _ _
5. So 77 x 84 = 6468.