Squaring numbers in the 500's
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- Choose a number in the 500s (start with low numbers at first;
then graduate to larger ones).
- The first two digits of the square are 25: 2 5 _ _ _ _
- The next two digits will be 10 times the last 2 digits: _ _ X X _ _
- The last two places will be the square of the last two digits: _ _ _ _ X X
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Example:
- If the number to be squared is 508:
- The first two digits are 25: 2 5 _ _ _ _
- The next two digits are 10 times the last 2 digits:
10 × 8 = 80: _ _ 8 0 _ _
- Square the last digit: 8 × 8 = 64: _ _ _ 6 4
- So 508 × 508 = 258,064.
For larger numbers reverse the steps:
- Square the last two digits (keep the carry):
_ _ _ _ X X
- 10 times the last two digits + carry: _ _ X X _ _
- 25 + carry: X X _ _ _ _
See the pattern?
- If the number to be squared is 525:
- Square the last two digits (keep the carry):
25 × 25 = 625 (keep 6): _ _ _ _ 2 5
- 10 times the last two digits + carry:
10 × 25 = 250; 250 + 6 = 256 (keep 2): _ _ 5 6 _ _
- 25 + carry: 25 + 2 - 27: 2 7 _ _ _ _
- So 425 × 425 = 275,625.
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