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how many positive four- digit integers have 3 as their tens digit and 5 or 9 as their ones digit?

i don't know where to begin

  • Mathematics -

    Start listing them. Four-digit numbers must be between 1000 and 9999. The last two numbers must be 35 or 39.
    ...etc., ending with
    There are 90 pairs of numbers, starting with 10 and ending with 99 as the first two digits.
    90 pairs = 180

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