Results 1 to 2 of 2

Thread: Please help

  1. #1
    Newbie
    Joined
    Aug 2006
    Posts
    8

    Question Please help

    I need help with this problem .


    15 divide 6 2/3 =?

    A) 100 1/4 B) 2 1/4 C)100 D) 2 3/4

    I'm thinking the letter D
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor Quick's Avatar
    Joined
    May 2006
    From
    New England
    Posts
    1,024
    Quote Originally Posted by Angel King
    I need help with this problem .


    15 divide 6 2/3 =?

    A) 100 1/4 B) 2 1/4 C)100 D) 2 3/4

    I'm thinking the letter D
    You know: $\displaystyle 15=\frac{15}{1}$ and $\displaystyle 6\frac{2}{3}=\frac{20}{3}$

    therefore we have equation: $\displaystyle \frac{15}{1}\div \frac{20}{3}$

    when dividing by a fraction you multiply by the reciprocal of the fraction, so we get: $\displaystyle \frac{15}{1}\div \frac{20}{3}=\frac{15}{1}\times \frac{3}{20}=\frac{15\times3}{1\times20}=\frac{45} {20}=2\frac{5}{20}=2\frac{1}{4}$

    so the answer is B, not d

    BTW When I was taught to divide fractions my teachers would say that you would "cross multiply" so you can think of it like this:

    $\displaystyle \frac{15}{1}\div\frac{20}{3}=\frac{15}{1}
    \!
    \!
    \nwarrow
    \!
    \!
    \!
    \!
    \!
    \!
    \swarrow
    \!
    \!
    \frac{20}{3}=\frac{15\times3}{1\times20}=\frac{45} {20}$

    did this post help?
    Last edited by Quick; Aug 24th 2006 at 10:12 AM.
    Follow Math Help Forum on Facebook and Google+


/mathhelpforum @mathhelpforum