Question

If $n\left(AUB\right)=15,n\left(A\right)=8$, $n\left(B\right)=9$, then $n(A-B)=$ _________?

• A. $6$
• B. $7$
• C. $2$
• D. $1$

Answer 1

Answer: (A)

$6$

now, as we know,

$n(A\cup B)=n\left(A\right)+n\left(B\right)-n(A\cap B)$

So, $n(A\cap B)=n\left(A\right)+n\left(B\right)-n(A\cup B)$

$=8+9-15$

$=2$

So, $n(A-B)=8-2=6$

$n(A-B=6$