Jagoan Matematika: Squaring numbers in the 40s

Jagoan Matematika

Gateway For Tour Brain Math

Sunday, May 20, 2007

Squaring numbers in the 40s

1. Square the last digit (keep the carry) _ _ X
2. Multiply the last digit by 8, add the carry _ X _
3. The first digits will be 16 plus the carry: X X _ _

Example:
1. If the number to be squared is 42:
2. Square the last digit: 2 × 2 = 4 _ _ _ 4
3. Multiply the last digit by 8: 8 × 2 = 16 _ _ 6 _
4. The first digits will be 16 plus the carry: 16 (+ carry): 16 + 1 = 17 1 7 _ _
5. So 42 × 42 = 1764.

See the pattern?

1. If the number to be squared is 48:
2. Square the last digit (keep the carry): 8 × 8 = 64 (keep 6) _ _ _ 4
3. Multiply the last digit by 8, add the carry: 8 × 8 = 64, 64 + 6 = 70 (keep 7) _ _ 0 _
4. The first digits will be 16 plus the carry: 16 (+ carry): 16 + 7 = 23 2 3 _ _
5. So 48 × 48 = 2304.

With some practice you will be giving these squares quickly.

posted by marhadi @ 6:40 AM

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