In a survey of a city, it was found that 90 percent of the people in the city own a refrigerator and 15 percent own a washing machine. If everybody owns at least one appliance, what percentage owns both?
(a)5 percent
(b)8 percent
(c)10 percent
(d)None of these
Answer
Answer (as printed): A
Explanation
$n(\mathrm{A})=90, n(\mathrm{B})=15, n(\mathrm{A} \cup \mathrm{B})=100$. So, $n(\mathrm{A} \cap \mathrm{B})=n(\mathrm{A})+n(\mathrm{B})-n(\mathrm{A} \cup \mathrm{B})$ $$=90+15-100=5 .$$ ∴ Percentage of people who own both $=5 \%$.