Question

If n(B) = 15, n(A B) = 25, and n(A B) = 3, find n(A).

Answer 1

When in doubt, draw a Venn diagram and fill in the numbers.

The easiest one to start is n(A∩B)=3.
Since n(B)=15, so n(B-A)=12.
n(A-B)=25-(12+3)=10.

Can you find n(A)?

Note:
To type the following symbols, type the characters following the symbol, but without the intervening spaces.
∩ & c a p ;
∪ & c u p ;
∈ & i s i n ;
⊂ & s u b ;
∉ & n o t i n ;

Answer 2

n(B) = 15 n(A∪B)=25, n(A∩B) = 3 find n(A)?

I thought A would equal 10

Answer 3

That's what I got too!