Tutorial 125 |
Multiplying two 2-digit numbers (difference of 2)
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- Choose a 2-digit number.
- Select a number either 2 smaller or 2 larger.
- Square the average of the two numbers.
- Subtract 1 from this square.
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Example:
- If the first number is 29, choose 31 as the second number.
- The average of 29 and 31 is 30. Square 30: 30 × 30 = 900.
- Subtract 1: 900 - 1 = 899.
- So 29 × 31 = 899.
See the pattern?
- If the first number is 76, choose 74 as the second number.
- The average of 76 and 74 is 75. Square 75: 75 × 75 = 5625.
- Subtract 1: 5625 - 1 = 5624.
- So 76 × 74 = 5624.
Practice this shortcut (remember your methods of squaring numbers).
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