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?
Solve/Investigate the Problem
I plan to use an equation to
solve the problem.
of the Problem
I let x = the unknown number. My equation was x + 129 = 2(x –
129). My solution was 387. Lisa said the solution was 43. Her
solution did not work in my equation. Upon comparing equations we disagreed
with the difference of 129 and the number. Discussion followed to determine
the meaning of the difference of 129 and the number. Did it mean x –
129 or 129 – x. The solution 387 did not meet the criteria stated in
the problem that number must be subtracted from 129. Thus the only solution
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