Using Cell Phones in a Mathematics Class
Study a touchtone phone's keypad, such as the one shown.
Suppose your phone number was 5552362. Imagine you are entering this number, focusing on the last four digits. This number is called a "triangular phone number" because when entering the last four digits, your fingers trace a triangle.
For a telephone number to be "triangular," the first and last digits must be equal.
Question 1: How many different triangular phone numbers are there?
Note, you will have to decide what "different" means in your solution of the problem...
 Do the telephone numbers ending in 2362, 2632, or 3623 form different triangles?
 Do the telephone numbers ending in 2362 and 5695 form different triangles?
Question 2: Can you find two triangular phone numbers that are "similar" but not "congruent"?
Question 3: By now using the last digit from the initial 3digit exchange, how many different quadrilateral phone numbers can you find? How many are squares? Rectangles? Rhombuses? Parallelopgrams? Trapezoids?
Question 3: By now using the last two digits from the initial 3digit exchange, how many different pentagonol phone numbers can you find? If regular, then you have a "golden" pentagonal telephone number!
Source: Adapted from Michael Contino, CMC ComMuniCator, Vol. 17#3, p. 58
Hint: Produce and compare lists as you build them...trying to be systematic.
Solution Commentary: Sorry, no answer is being provided....I'm too busy calling my "square" friends!
