For Geeks & Brainiacs #29- Green-Eyed Girls -
There's a small school where students have very unusual traits:
60% are girls
70% have green eyes
80% have blonde hair
At a minimum, what percentage of students are girls with green eyes and blonde hair?
ANSWER: The minimum percentage is 10%.
EXPLANATION: For simplicity, let's say there are 100 students at the school. This would mean 60 students are girls and 40 are boys. 70 students would have green eyes and at most 40 of those could be boys. So at a minimum, there are 30 girls with green eyes. 80 students have blonde hair so 20 students have non-blonde hair. Of the minimum 30 girls with green eyes, at most 20 of those could have non-blonde hair. So at a minimum, there are 10 girls with green eyes and blonde hair, or 10% of the 100 students.