Mathematics

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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.
    1035
    1039
    1135
    1139
    ...etc., ending with
    9935
    9939.
    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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