A pair of Brain Teasers for Tuesday. If you’re a teacher, consider putting these up as a warm-up at the start of class.
Teaser # 1) Poor Mr. and Mrs. Household. They have 10 boys, and each of their sons has one sister. How many children do Mr. and Mrs. Household have altogether?
Teaser #2) While keeping track of their many children’s height, Mr. and Mrs. Household notice that one of their sons has an unusual characteristic — his height doubles every year until he reaches age 13, at which time he abruptly stops growing. How many years did it take this boy to reach one quarter of his maximum height?
Answer #1) Eleven children, for only one girl is required in order for each boy to have one sister.
Answer #2) The boy would reach 1/4 of his maximum height when he has his 11th birthday. Since his height doubles every year, he had to be half of his maximum height on his 12th birthday. And so he had to be half of that — or 1/4 of his final height — on his 11th birthday.
- 10 Websites for Puzzles, Brain Teasers and Riddles (makeuseof.com)