David Rock's House Number
David's house has a number.
1) If the house number is a multiple of 3, then it is a number from 50 to 59
2) If the house number is NOT a multiple of 4, then it is a number from 60 to 69
3) If the house number is NOT a multiple of 6, then it is a number from 70 to 79
What is the house number? Note: Conditions 1), 2), and 3) must all be satisfied.
Will the problem have a unique solution if the interval in 3) is changed from 80 to 89?
Can you create similar problems with other intervals, having unique solutions?
Who is David Rock?
David is a mathematics educator who happens to be Dean, College of Education, University of Mississippi. He is co-author of Teaching Secondary Mathematics, one of the most widely used current mathematics methods textbooks.