Beacon Lesson Plan Library

How Old Did You Say?

Christy Clanton
Bay District Schools


How Old Did You Say? What an interesting way for students to see and develop algebraic formulas based on their own ages as the known variable.


The student generalizes a pattern, relation, or function to explain how a change in one quantity results in a change in another.


-Whiteboard and markers
--How Old Are You?- Sheet
-Student pencils


1. Gather materials
2. Write -teacher age formula description-


1. The teacher asks the class to guess her age. Students give estimates, which the teacher records on the whiteboard.
2. Then the teacher tells them that she will give them a formula for calculating the answer. Teacher shares an appropriate formula. Example: I was 26 years old when my daughter was born and 36 years old when my son was born. My daughter was 10 years old when my son was born. My son is 6 years old. How old am I?
Orally, the teacher develops and writes this on the whiteboard, as if -thinking out loud:-
My son = 6, which I will call -A- for Aubrey.
My daughter is Corinna, so I will call her -C- for short, since mathematicians are people of few words.
I will call me Mom, or -M- for short.

So how does A (Aubrey's age) compare to C (Corinna's age) and to M (my age)?

Develop with the children that:
M= A + 36
M = C + 26
C = A + 10
3. The teacher asks the class to complete the biographical data on their -How Old Are You?- Sheet and write their own challenge for the class. These challenges can then be placed on a board for other students to try to solve.


Teacher assesses student-created charts and challenge compositions.
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