20-CS-110-001 Introduction to Computer Science Fall 2010

Solution to Pencil Prices Puzzle

    This is a variation of a sequence called the Fibonacci Sequence. You can use some algebra to work backwards or simply use some trial and error to see what the starting numbers are in the sequence. The eighth number in the sequence should be the value of 60 to allow for six increases that are equal to the sum of the previous two numbers. The sequence should look like this: 1, 4, 5, 9, 14, 23, 37, 60, 97. Therefore, a pencil costs $0.97 today and, counting backwards seven years, a pencil costs $0.04 seven years ago.