Find the difference of the squares of two
               different 2-digit numbers

1. Select two consecutive 2-digit numbers, one not more than 10 larger than the other (experts need not use this limitation).
2. Subtract the smaller number from the larger.
3. Add the two numbers.
4. Multiply the first answer by the second.

   Examples:

1. If 71 and 64 are selected:
2. 71 - 64 = 7.
3. 71 + 64 = 135
   (Add left to right: 71 + 64 = 71 + 60 + 4 = 131 + 4 = 135)
4. Multiply these results: 7 x 135 = 945
   (Multiply left to right: 7 x 135 = 7 x (100+30+5) =
   700 + 210 + 35 = 910 + 35 = 945)
5. So the difference of the squares of 71 and 64 is 945.

   See the pattern?

1. If 27 and 36 are selected:
2. 36 - 27 = 9.
3. 36 + 27 = 63
   (Think: 27 + 30 + 6 = 57 + 6 = 63)
4. Multiply these results: 9 x 63 = 567
   (Think: 9 x (60+3) = 540 + 27 = 567)
5. So the difference of the squares of 27 and 36 is 567.

Practice multiplying and adding from left to right and this will become an easy but impressive mental math feat.