Prime Factor

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candygal79 Senior | Next Rank: 100 Posts
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Prime Factor

Post Fri Apr 04, 2014 12:22 am
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    What is the sum of different positive Prime Factor of 550 ?

    A 10

    B 11

    C 15

    D 16

    E 18

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    Post Fri Apr 04, 2014 12:30 am
    candygal79 wrote:
    What is the sum of different positive Prime Factor of 550 ?

    A 10

    B 11

    C 15

    D 16

    E 18
    550 = (2)(5)(5)(11)
    So, the DIFFERENT prime factors are 2, 5 and 11
    2 + 5 + 11 = 18 = E

    Cheers,
    Brent

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    Post Fri Apr 04, 2014 1:29 pm
    Hi candygal79,

    There's a math rule called 'prime factorization' that you might occasionally use on the GMAT. The idea is that any positive number can be "broken down" into a bunch of prime numbers that are multiplied together (unless the number is already prime).

    eg 10 = 2x5

    Here, we're asked to prime factor 550; this can be done in a set of steps.

    550 = 55x10

    55 = 5x11
    10 = 2x5

    So 550 = 2x5x5x11

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    Abhishek009 Master | Next Rank: 500 Posts
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    Post Sat Apr 05, 2014 7:12 am
    candygal79 wrote:
    What is the sum of different positive Prime Factor of 550 ?

    A 10

    B 11

    C 15

    D 16

    E 18
    Find the factors of 550

    550 = 5^2 X 2 X 11

    Now we are required to find only the sum of different positive Prime Factor of the number , so the sum is -

    5 + 2 + 11 => 18

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    Abhishek

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