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Math Help - understanding SAT problem

  1. #1
    Junior Member Dergyll's Avatar
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    understanding SAT problem

    Hey guys

    Just need to know, on the SAT/PSAT, a phrase called "Units digit" keeps popping up and I have no idea what it means...Here is an example problem

    "The unit digit of the sum of three consecutive integers is 8. What is the units digit of the least of these integers?"

    A) 4
    B) 5
    C) 6
    D) 7
    E) 8

    I know this is noobie stuff but just need to know what it means real quick

    Thanks alot
    Derg
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  2. #2
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by Dergyll View Post
    Hey guys

    Just need to know, on the SAT/PSAT, a phrase called "Units digit" keeps popping up and I have no idea what it means...Here is an example problem

    "The unit digit of the sum of three consecutive integers is 8. What is the units digit of the least of these integers?"

    A) 4
    B) 5
    C) 6
    D) 7
    E) 8

    I know this is noobie stuff but just need to know what it means real quick

    Thanks alot
    Derg
    The "units digit" of a number is the same as the "ones digit": it is the digit of a number that corresponds to how many times 1 you have.

    Probably not a good explanation. Here are some examples:
    1234 The "units digit" is 4
    5678 The "units digit" is 8

    -Dan
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  3. #3
    Junior Member Dergyll's Avatar
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    Wow dan thanks a million, you really saved my hide with this...

    Now this clears everything apart

    Thanks again
    Derg
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  4. #4
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by Dergyll View Post
    Hey guys

    Just need to know, on the SAT/PSAT, a phrase called "Units digit" keeps popping up and I have no idea what it means...Here is an example problem

    "The unit digit of the sum of three consecutive integers is 8. What is the units digit of the least of these integers?"

    A) 4
    B) 5
    C) 6
    D) 7
    E) 8

    I know this is noobie stuff but just need to know what it means real quick

    Thanks alot
    Derg
    Let the first number be x. Then the three numbers are x, x + 1, and x + 2. The sum of these is 3x + 3. Call the units digit of x n. So the units digit of the sum will be
    3n + 3 = 8 (If 3n + 3 is not greater than 9)
    or
    3n + 3 - 10 = 3n - 7 = 8 (else)

    In the first case we have:
    3n + 3 = 8

    3n = 5 <-- No such n exists.

    In the second case we have:
    3n - 7 = 8

    3n = 15

    n = 5.

    Thus the units digit of x (the least of the three numbers) is 5.

    -Dan
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