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Thread: quicker method??

  1. #1
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    quicker method??

    If
    p is the product of the integers from 1 to 30, inclusive, what is the greatest integer k for which 3k is a factor of p?
    A. 10
    B. 12
    C. 14
    D. 16

    E. 18

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    The question seems a bit weird.
    If pis the product of all integers from 1 to 30 that is 30!, then k can be much higher.Of call the given choices I would choose 18. Cause 18 is one of the integers in the product p.

    Can you confirm this question ?

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    The question is asking how many factors of 3 are in 30!

    30/3 = 10
    30/3^2 =3
    30/3^3=1

    Therefore, the answer is 10+3+1=14

    Answer C

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    The question is mistyped. It should be:

    If p is the product of the integers from 1 to 30, inclusive, what is the greatest integer k for which 3^k is a factor of p ?

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    An Urch Guru Pundit Swami Sage Fiver's Avatar
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    Subsequent to the correction by BoB.
    30/3=10
    10/3=3
    3/3=1
    Therefore 10+3+1=14
    Basically we are looking at multiples of 3 hence that many number of 3s (i.e. 10) and other ways in which a 27 can be formed (e.g. 9 *3) etc.

    C is my answer.

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    C for me too
    Following method can be used to calculate this

    30/3 = 10
    10/3 = 3
    3/1 = 1
    Answer 10+3+1 = 14

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    Quote Originally Posted by NishantG View Post
    C for me too
    Following method can be used to calculate this

    30/3 = 10
    10/3 = 3
    3/1 = 1
    Answer 10+3+1 = 14
    For those unaware of this formula it simply comprehends to :

    How many factors of 3 in 30! - [3,6,9,,,30] = [30/3] = 10
    How many factors of 9 in 30! - [9,18,27] = [30/9] = 3
    How many factors of 27 in 30! - [27] = [30/27] = 1

    where 30! = 1x2x3x...30

    ANs = 10+3+1
    Hey Harvard, I am right here!!
    rep me if I made some sense

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    Thanks BoB for the correction in the question otherwise I was just wondering how to approach about it.

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