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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

I will need to set up an equation where one side shows a number (n) added to 129 on one side, and 2 times 129 – the number (n).  When I solve the equation, I should come up with a number to solve both sides of the equation.

 

Plans to Solve/Investigate the Problem

In class, we set up an equation to solve the problem.  We also used Excel to help us discover the answer.  If we did it successfully, we should be able to find one number that will satisfy the equation.

 

Investigation/Exploration of the Problem

The first thing I did was to use Excel to compare numbers.  Below is the Excel sheet I used.

 

N

N + 129

129 - N

2(129-N)

50

179

79

158

51

180

78

156

52

181

77

154

49

178

80

160

47

176

82

164

45

174

84

168

43

172

86

172

I tried 50 as “n”, then tried the next 2 higher numbers, to try to get the two yellow columns equal.  When the difference between those numbers was getting higher by raising the value of “n”, I tried lowering the value of “n”.  The two columns started getting closer in numbers.  I finally found 43 as the answer; If n = 43, then 43 + 129 = 2 (129 – 43).  172 = 86 * 2 or 172. 

 

Next we tried writing an equation.  This was easy to do, because I’d already done most of the work using Excel.  N + 129 = 2 ( 129 – N)

N + 129 = 258 – 2N

3N = 129

N = 43

 

Author & Contact
Meg Ramsey
mramsey@rockdale.k12.ga.us

Link(s) to resources, references, lesson plans, and/or other materials
Solving an Equation
Link 2

 

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