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(129N)

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
U
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