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A Question of Pass/Fail %

  • 18-05-2011 8:38pm
    #1
    dory
    Moderators, Recreation & Hobbies Moderators Posts: 4,575 Mod ✭✭✭✭


    Hello all. Hypothetical question here.... :o

    If someone got 21% in an exam, and that exam was worth 30% of their overall grade, what percentage would that person need in the main exam (worth 70%) to get a 40% average?

    And the 21% was not in maths...


Comments

  • #2
    D-Generate
    Registered Users, Registered Users 2 Posts: 2,945 ✭✭✭D-Generate


    48.14% in the main exam.


  • #3
    red_fox
    Registered Users, Registered Users 2 Posts: 642 ✭✭✭red_fox


    Imagine you are see a bucket with 30 red apples, and another with 70 green apples.

    You are given 21% of the apples from the first bucket and you need at least 40 apples to feed your family, what percentage of the green apples do you need?

    (the point of this post is to remove one of the percentages because looking at a percentage of a percentage might be confusing)


  • #4
    dory
    Moderators, Recreation & Hobbies Moderators Posts: 4,575 Mod ✭✭✭✭dory


    Very nice red fox! 48.1 is grand. Phew! Thanks people!


  • #5
    LeixlipRed
    Closed Accounts Posts: 6,081 ✭✭✭LeixlipRed


    Hypothetical me arse :D Hope these aren't maths exams you're doing ;) Always makes me scratch my head when students ask me in the last class can I work out their CA grade for them!


  • #6
    Michael Collins
    Moderators, Science, Health & Environment Moderators Posts: 1,852 Mod ✭✭✭✭Michael Collins


    LeixlipRed wrote: »
    Hypothetical me arse :D Hope these aren't maths exams you're doing ;) Always makes me scratch my head when students ask me in the last class can I work out their CA grade for them!

    Answer: If you have to ask, you don't wanna know!


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  • #7
    LeixlipRed
    Closed Accounts Posts: 6,081 ✭✭✭LeixlipRed


    No, it's not that that annoys me, it's the fact they can't compute it themselves that's worrying :D


  • #8
    **Timbuk2**
    Moderators, Education Moderators, Motoring & Transport Moderators Posts: 7,396 Mod ✭✭✭✭**Timbuk2**


    People ask me this question all the time - it's easy to explain if you think of it like red_fox, or if you write it as an algebraic expression.

    40 = (0.3)(21) + (0.7)(x)
    (x represents the percentage you would need to score in the main exam to get 40% overall)

    Solving for x gives x=48.14%.


  • #9
    Michael Collins
    Moderators, Science, Health & Environment Moderators Posts: 1,852 Mod ✭✭✭✭Michael Collins


    LeixlipRed wrote: »
    No, it's not that that annoys me, it's the fact they can't compute it themselves that's worrying :D

    Yeh, that's what I was trying to imply!


  • #10
    LeixlipRed
    Closed Accounts Posts: 6,081 ✭✭✭LeixlipRed


    Ah sorry, I thought you were implying they had just done badly!


  • #11
    Michael Collins
    Moderators, Science, Health & Environment Moderators Posts: 1,852 Mod ✭✭✭✭Michael Collins


    LeixlipRed wrote: »
    Ah sorry, I thought you were implying they had just done badly!

    Well come to think of it it's probably not just the bad students that can't work this kinda thing out. You seem to get a lot of students who are good at doing exams but when it comes to applying maths to real situations, such as this one, often fail.


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  • #12
    LeixlipRed
    Closed Accounts Posts: 6,081 ✭✭✭LeixlipRed


    Yep, it's not just the poor students.


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