Algebra Lesson 8 – The Equation Behind an Old Trick
by Elaine Ernst Schneider
To understand why the puzzle works, you must solve it algebraically.
Let x = your house number.
Let y = your age.
Let A = answer
Using the numbered list of instructions, set up the problem as an algebraic equation. It would look like this:
A = 50(2x + 5) + y + 365 – 615
A = 100x + 250 + y +365 -615
A = 100x + y
A = x + y/100
x = the house number (You started with this number.)
y/100 = your age (When you divide by 100, you move the decimal point two places to the left.)
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