Tutorial 129 |
Multiplying two 2-digit numbers (difference of 8)
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- Choose a 2-digit number.
- Select a number either 8 smaller or 8 larger.
- Find the middle number of the two (the average).
- Square this middle number (multiply it by itself).
- Subtract 16 from this square.
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Example:
- If the first number is 34, choose 26 as the second number (8 smaller).
- The middle number (the average) is 30.
- Square this middle number: 30 × 30 = 900.
- Subtract 16 from this square: 900 - 16 = 884.
- So 34 × 26 = 884.
See the pattern?
- If the first number is 64, choose 72 as the second number (8 larger).
- The middle number (the average) is 68.
- Square this middle number: 68 × 68 = 4624. Remember
how to square a 2-digit number ending in 8?
- Subtract 16 from this square: 4624 - 16 = 4608.
- So 64 × 72 = 4608.
Choose the second number that will give you the easier square, and use your square
shortcuts. Practice!
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