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

• Jan 15th 2013, 04:48 AM
matrix37696
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.
• Jan 15th 2013, 11:11 AM
Barioth
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!?
• Jan 16th 2013, 03:52 AM
matrix37696
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.