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Finding digits using divisibility tests
- The last digit of a square of a natural number is odd. What
can the next-to-last digit be equal to?
- The next-to-last digit of a perfect square is odd. What can
be the last digit?
- Write single digits in the blanks to make a four-digit
number that’s a multiple of 15:
___ 1 5 ___
- How many four-digit numbers with 97 in the middle are
multiples of 45?
Answers
- Next-to-last digit can be any even digit: 0, 2, 4, 6, or 8.
- Only 6.
- If the last digit is 0, the first one can be 3, 6, or 9.
If the last digit is 5, the first digit can be 1, 4, or 7.
- Only two: 2970 and 6975.
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