Oh, hello there.
Well then, If 70% of students have blank paper, 30% have both lined and blank paper, and 10% no paper, how many people have just lined paper?
Thanks.
Let Set B=students who have blank paper, $\displaystyle P(B)=0.7$
Set L=students who have lined paper, $\displaystyle P(L)=x$
$\displaystyle P({B}\cap{L})=0.3$
$\displaystyle P(not {B}\cup{L})=0.1$
That is, the set of students without paper.
You should draw a Venn diagram illustrate this
$\displaystyle P({B}\cup{L})=1-0.1=0.9$
$\displaystyle P({B}\cup{L})=P(B)+P(L)-P({B}\cap{L})=0.9$
$\displaystyle 0.7+x-0.3=0.9$
$\displaystyle x=0.5$
$\displaystyle P(L)=0.5$
To determine percentage of people with lined paper
$\displaystyle P(L(alone))=P(L)-P({L}\cap{B})=0.5-0.3=0.2$
you have
B denoted to Blank just
L denoted to lined just
N denoted to no paper
$\displaystyle P(B\cup L) = .9 $ since there is just 10% have not paper
$\displaystyle P(B\cap L) = .3 $ since there is 30% have blank and lined
$\displaystyle P(B) = .7 $ since there is 70% have just the blank
use
$\displaystyle P(A\cup B) = P(A) + P(B) - P(A\cap B ) $
I think it is now easy