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Math Help - Getting the intersection of three sets - but very little information given!

  1. #1
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    Getting the intersection of three sets - but very little information given!

    A survey of 1000 people found that 70% of the people have a CD player, 85% have a telephone and 45.2% have a computer. At least how many people have all three objects?

    Well as you can see, this question has me puzzled ( I am a weak computer science student, mathematically). Normally these questions give a bit more to go on like 40 have a pc and cd player etc.

    Any help, or guide in the right direction would be great,

    thanks everyone,

    m.
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  2. #2
    Junior Member Barioth's Avatar
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    Re: Getting the intersection of three sets - but very little information given!

    Hi

    Let's say

    A is the groupe of student with a Cd player.
    B is the groupe of student with a telephone.
    C is the groupe with a computer.

    |A| = 700 = Card A
    |B| = 850 = Card B
    |C| = 452 = Card C

    you looking for |A and B and C|

    I would start finding |A and B| (the minimum of this is 550.) To find 550 here is what I did
    |Non A| = 1000-700 = 300.
    |B| -|Non A| = 550

    You do the same thing with |(A and B) and C| the minimum value of this, if I didn't mess up. is 2.

    Hope that helped!?
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  3. #3
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    Re: Getting the intersection of three sets - but very little information given!

    That's brilliant, thanks for your help Barioth!!! actually you explained it better than our lecturer!!
    thanks again,
    m.
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