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 Write-up

Title
Double Trouble

Problem Statement
What number can you add to 129 and subtract from 129 such that the sum of the number and 129 is twice the difference between 129 and the number?

Problem setup

This problem is asking for you to come up with the number that will satisfy the requirements.  The easiest way to do this is by coming up with an equation.

Plans to Solve/Investigate the Problem

My initial strategy was to construct an equation based on the wording of the problem to come up with the answer.  I decided to name the number x.

Investigation/Exploration of the Problem

The equation that I came up with was (x+129)=2(129-x).  This equation is solved as follows:

(x+129)=2(129-x).

x+129=258-2x

-129  -129

x=129-2x

+2x  +2x

3x=129

x=43

43 is our answer because the sum of 43 and 129 is twice the difference between 129 and the 43.

43+129 = 172    129-43=86    86(2)=172

Author & Contact
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Link(s) to resources, references, lesson plans, and/or other materials
Hotmath