Aunt Janice was extremely touchy about her age. When an impudent nephew was brave enough to ask her, she cunningly replied that she was 35 years old, not counting Saturdays or Sundays. So how old was she? -Another puzzle from Mo Page
Seven students came up with the following: There are 104 weekend days in a year, so she’s omitting (35 years)(104 weekend days/year) = 3640 omitted days, or nearly 10 omitted years. So Aunt Janice’s true age is 45.
Everyone’s satisfied. No other answers, no tugs of insecurity about the reasoning.
The puzzle: what do you say to them to get them to see that their answer doesn’t make sense? Remember, the goal is not to explain the correct answer well, the goal is to point out something that leads them to find the flaw in this one (or at least recognize that it’s flawed).