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Project Maths Question

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  • 20-12-2011 5:16pm
    #1
    John 10
    Registered Users Posts: 14 ✭


    Hi everyone, I have my maths xmas test tomorrow and i'm doing some revision in the exam papers and i'm stuck on this question and it's gotten the better of me!:( Can anyone help?

    There are 16 girls and 8 boys in a class. Half of these 24 students study French. The probability that a randomly selected girl studies French is 1.5 times the probability that a randomly selected boy studies French. How many of the boys in the class study French?

    Thanks in advance!


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    #2
    Canard
    Moderators, Education Moderators Posts: 8,572 Mod ✭✭✭✭Canard


    That one got me too! Still dont get it...what I did was look up the solution on examinations.ie, it didnt make a whole lot of sense to me but its better than nothing I suppose.

    Sorry I cant help you more :o


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    #3
    John 10
    Registered Users Posts: 14 ✭John 10


    Ah yes never thought of the solutions on examinations.ie!:rolleyes:

    Makes sense now. Have to say some of the questions on the papers are very hard and awkward as well, they really are doing their upmost best to make a balls of the subject. Suppose it doesn't help when I haven't done a whole lot of revision and our teacher gives us tests that aren't exactly exam material!


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    #4
    Canard
    Moderators, Education Moderators Posts: 8,572 Mod ✭✭✭✭Canard


    Exactly my thoughts! I get A's in class tests but when it comes to exam style questions I freak out :o The books need to be more exam-focused or the exams need to be dumbed down some more :P


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    #5
    equivariant
    Registered Users Posts: 966 ✭✭✭equivariant


    John 10 wrote: »
    Hi everyone, I have my maths xmas test tomorrow and i'm doing some revision in the exam papers and i'm stuck on this question and it's gotten the better of me!:( Can anyone help?

    There are 16 girls and 8 boys in a class. Half of these 24 students study French. The probability that a randomly selected girl studies French is 1.5 times the probability that a randomly selected boy studies French. How many of the boys in the class study French?

    Thanks in advance!

    Let x be the number of boys that study French. We want to somehow write down a equation in x that we can solve.

    In terms of x, how many girls study French? To answer this, use the fact that we are told that 12 students in total study French.

    Now P(random boy studies French) = x/8 (make sure you understand why this is true)

    Now, we are told that P(random girl studies French) = 1.5 x P(random boy studies french). So P(random girl studies French) = 1.5(x/8)

    But P(random girl studies French) = (number of girls who study French)/16

    Now express the right hand side of the last equation in terms of x.

    Now try to put it all together and solve for x.


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    #6
    kcull
    Registered Users Posts: 9 ✭kcull


    equivariant wrote: »

    But P(random girl studies French) = (number of girls who study French)/16

    I'm with you until here but why is P(random girl studies French) = (number of girls who study French)/16???? totally confused


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    #7
    Johnny Jukebox
    Registered Users Posts: 655 ✭✭✭Johnny Jukebox


    kcull wrote: »
    I'm with you until here but why is P(random girl studies French) = (number of girls who study French)/16???? totally confused

    There are 16 girls in total.

    As an example, say 4 of them study French...

    So P(random girl studies French) is 4/16 - now forget the example.

    But you don't know how many girls study French - but you do know 12 in total study French and that x of that 12 are boys so...

    P(random girl....) = (12 - x)/16


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