Multiplying Two digit Numbers With difference of 10

1. Choose a 2-digit number.
2. Select a number either 10 smaller or 10 larger.
3. Find the middle number of the two (the average).
4. Square this middle number (multiply it by itself).
5. Subtract 25 from this square.

Example:

1. If the first number is 36, choose 26 as the second number (10 smaller).
2. The middle number (the average) is 31.
3. Square this middle number: 31 × 31 = 961. (Remember how to square a 2-digit number ending in 1?)
4. Subtract 25 from this square: 961 - 25 = 936
   (subtract mentally in steps: think 961 - 20 - 5 = 941 - 5 = 936).
5. So 36 × 26 = 936.