# numbers of elements in a set

• March 6th 2009, 02:25 PM
zhupolongjoe
numbers of elements in a set
For this |A| is the number of elements in A.

So we are given:

|A|=24, |B|=21, |AUB|=37, |A intersect C|=11, |B-C|=10 and |C-B|=12

We need to find:

a)|B-A|

b)|BUC|

c) |C|

I know that we can use |AUB| =|A|+|B|-|A intersect B| to find how many elements in A intersect B, but the subtraction part is throwing me off.
Any ideas? Thank you.
• March 6th 2009, 02:32 PM
HallsofIvy
Quote:

Originally Posted by zhupolongjoe
For this |A| is the number of elements in A.

So we are given:

|A|=24, |B|=21, |AUB|=37, |A intersect C|=11, |B-C|=10 and |C-B|=12

We need to find:

a)|B-A|

b)|BUC|

c) |C|

I know that we can use |AUB| =|A|+|B|-|A intersect B| to find how many elements in A intersect B, but the subtraction part is throwing me off.
Any ideas? Thank you.

$A-B= A\cup B- A\cap B$
$|A-B= |A\cup B|- |A\cap B|$
• March 6th 2009, 02:41 PM
zhupolongjoe
Ok, so |A-B|=37-8=29

How do we get B-A from that, is it just like 37-29?