In a town, 40% of the people have brown hair, 25% have brown eyes, and 10% have both brown hair and brown eyes. What percentage of people in the town have neither brown hair nor brown eyes?
Answer: B
Let H be the set for brown hair and E for brown eyes.
n(H) = 40%, n(E) = 25%, n(H ∩ E) = 10%.
Percentage of people with at least one trait = n(H ∪ E) = n(H) + n(E) - n(H ∩ E) = 40% + 25% - 10% = 55%.
Percentage of people with neither trait = 100% - n(H ∪ E) = 100% - 55% = 45%.