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anonymous

  • one year ago

The number of two-digit positive integers for which the units digit is not equal to the tens digit.

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  1. misty1212
    • one year ago
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    HI!!

  2. anonymous
    • one year ago
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    hi misty =)

  3. misty1212
    • one year ago
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    my guess is \(81\) reason as follows: you have nine choices for the tens place digit (it cannot be zero) then another 9 choices for the ones place (it can be zero, but it cannot be the tens digit)

  4. misty1212
    • one year ago
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    by the counting principle you get \(9\times 9=81\)

  5. anonymous
    • one year ago
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    ouuuuu niceeeee okay got it thanks!

  6. misty1212
    • one year ago
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    course i could be wrong maybe @geerky42 has a different answer

  7. anonymous
    • one year ago
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    it was right

  8. geerky42
    • one year ago
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    There are \(99-10+1 = 90\) two digits numbers. Now exclude numbers where tens digit and unit digit are same; 11, 22, 33, 44, ..., 99 There are \(9\) of them. So you have \(90-9 = \boxed{81}\) So @misty1212 is correct.

  9. anonymous
    • one year ago
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    hey why do u exclude the 11, 22,33,44 etc.?????

  10. misty1212
    • one year ago
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    for which the units digit is not equal to the tens digit.

  11. anonymous
    • one year ago
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    but doesnt that just mean 10, 20, 30, 40 etc?

  12. geerky42
    • one year ago
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    No. "units digit is equal to the tens digit" means 11, 22, 33, etc. So here, we have "units digit is NOT equal to the tens digit", which means 10, 12, 13, ..., 20, 21, 23, ..., 31, 32, 34, ..., etc.

  13. geerky42
    • one year ago
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    We counted ALL two digits numbers, then we un-counted number where "units digit is equal to the tens digit"

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