Answer:
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Three-digit integer in the form of abc.
Possible numbers for each digit
- a - 1 to 9, nine options,
- b and c - 0 to 9, ten options
Let a = 5 or 7, then for a we have 2, for b and c 10 options:
Let b = 5 or 7, then for a we have 9 - 2 = 7, for b 2 and for c 10 options
Let c = 5 or 7, then for a we have 9 - 2 = 7, for b 10 - 2 = 8 and for c 2 options
Total options
