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Lesson Tutor : Elaine Ernst Schneider : Lesson Plans : Mathematics : Algebra : Grade 9

  /  Lesson Tutor : Elaine Ernst Schneider : Lesson Plans : Mathematics : Algebra : Grade 9

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

ANSWER:

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

100
A = 100x + 250 + y +365 -615

100
A = 100x + y

100
A = x + y/100
Therefore,

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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