Jagoan Matematika: Squaring numbers in the 20s

Jagoan Matematika

Gateway For Tour Brain Math

Sunday, May 20, 2007

Squaring numbers in the 20s

1. Square the last digit (keep the carry) _ _ X
2. Multiply the last digit by 4, add the carry _ X _
3. The first digit will be 4 plus the carry: X _ _

Example:

1. If the number to be squared is 24:
2. Square the last digit (keep the carry): 4 × 4 = 16 (keep 1) _ _ 6
3. Multiply the last digit by 4, add the carry: 4 × 4 = 16, 16 + 1 = 17 _ 7 _
4. The first digit will be 4 plus the carry: 4 (+ carry): 4 + 1 = 5 5 _ _
5. So 24 × 24 = 576.

See the pattern?

1. If the number to be squared is 26:
2. Square the last digit (keep the carry): 6 × 6 = 36 (keep 3) _ _ 6
3. Multiply the last digit by 4, add the carry: 4 × 6 = 24, 24 + 3 = 27 (keep 2) _ 7 _
4. The first digit will be 4 plus the carry: 4 (+ carry): 4 + 2 = 6 6 _ _.
5. So 26 × 26 = 676.

posted by marhadi @ 6:33 AM

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