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anonymous

  • 5 years ago

Internal telephone numbers in a university are composed of 5 digits. The first two digits can form any integer between (and including) 61 and 75, the third digit is an integer between 1 and 9 and the last two each take any integer value. Assume that it is disallowed to have a phone number with last three digits being 100, 101, or 102. In such case, the total number of possible internal telephone numbers that start with the digit 7 is.....

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  1. anonymous
    • 5 years ago
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    is it 4500 - 15 = 4485

  2. amistre64
    • 5 years ago
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    75 61 --- 14+1 = 15 ways 1 to 9 = 9 ways (if we can count 1 and 9) 1000 ways - 3 = 997 ways for the ending 15*9*997 is what it looks like to me

  3. amistre64
    • 5 years ago
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    is 134,595 an option?

  4. anonymous
    • 5 years ago
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    the first digit starts with a 7 mate, so its 5 possible choices times by 9 possible choices times by 100 possible choices for the last 2 digits including "00", since i have to avoid 100,101,102, i got to take of 15 possibilities so its 4500-15 = 4485

  5. amistre64
    • 5 years ago
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    yeah, start with a 7 ... to many numbers to sort thru lol 70 71 72 73 74 75 = 6 ways then 6.9.997 is what I would see then

  6. amistre64
    • 5 years ago
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    the last 3 digits can be from 000 to 999 (1000), excluding the 3 ways mentioned = 997 ways

  7. amistre64
    • 5 years ago
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    61 to 75 = 15 ways, exclude the 6s and we get 6 ways to start

  8. amistre64
    • 5 years ago
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    53,838 an option?

  9. anonymous
    • 5 years ago
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    so its 5400 - 18 = 5382, its not multiple choice =\

  10. amistre64
    • 5 years ago
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    wait, im still reading the question a little off. try this:

  11. amistre64
    • 5 years ago
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    composed of 5 digits. first two digits, starts with a 7: 7 __ 6 ways 3rd digit between 1 and 9: 9 ways last two digits each take any integer value. Assume that it is disallowed to have a phone number with last three digits being 100, 101, or 102

  12. amistre64
    • 5 years ago
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    100 to 999 is where I was off at,

  13. amistre64
    • 5 years ago
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    000 to 099 is 100 excluded ways, + the 3 mentioned total 103 excluded ways 1000 103 ----- 897 ways total then sound right?

  14. amistre64
    • 5 years ago
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    im still including that 3rd digit ....

  15. amistre64
    • 5 years ago
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    00 to 99 is the last 2 digit options (100); exclude 00,01,02 (-3) 100-3 = 97 ways 6.9.97 = 5238

  16. anonymous
    • 5 years ago
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    thanks 5382 right? was that a typo error?

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