Lesson Tutor : Lesson Plans : Mathematics : Algebra : Grade 9

Algebra Lesson 8 – The Equation Behind an Old Trick
by Elaine Ernst Schneider

Objective(s): By the end of this lesson the student will be able to: 

Pre-Class Assignment: Review/ completion of Algebra Lesson 7

Resources/Equipment/Time Required: 


In the last lesson, you learned that equations can be used to solve puzzles. For years, mathematicians have been solving the following puzzle to the amazement of their students. Not only is it a fun “trick,” but it is based on a sound mathematical principle that makes it work:

By using your house number, a mathematician can calculate your age!

Here’s how it works:

1.Double your house number.
2.Add 5.
3.Multiply by 50.
4.Add your age.
5.Add the number of days in a year (365).
6.Take that number and subtract 615.
7.Pretend it is an amount of money and position the decimal point for dollars and cents.

Answer: the dollars will be your house number and the cents will be your age.

But now the big question is: HOW does it work? Give it a little thought before looking at the answer.

Assignment(s) including Answer key:   Complete above then check here

Pre-Requisite To: Algebra Lesson 9

For more Articles by this Author, Click Here
For more Lesson Plans in the Subject: Algebra, Click Here