Multiplying Two digit Numbers With difference of 2

1. Choose a 2-digit number.
2. Select a number either 2 smaller or 2 larger.
3. Square the average of the two numbers.
4. Subtract 1 from this square.

Example:

1. If the first number is 29, choose 31 as the second number.
2. The average of 29 and 31 is 30. Square 30: 30 × 30 = 900.
3. Subtract 1: 900 - 1 = 899.
4. So 29 × 31 = 899.