| Sunday, May 20, 2007 |
| Squaring a 2-digit number ending in 5 |
1. Choose a 2-digit number ending in 5.
2. Multiply the first digit by the next consecutive number.
3. The product is the first two digits: XX _ _.
4. The last part of the answer is always 25: _ _ 2 5.
Example:
1. If the number is 35, 3 × 4 = 12 (first digit times next number). 1 2 _ _
2. The last part of the answer is always 25: _ _ 2 5.
3. So 35 × 35 = 1225.
See the pattern?
1. For 65 × 65, 6 × 7 = 42 (first digit times next number): 4 2 _ _.
2. The last part of the answer is always 25: _ _ 2 5.
3. So 65 × 65 = 4225. |
posted by marhadi @ 6:15 AM  |
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