Question 290884
If a concentration of a solution was 0.15 moles/liter 7 minutes after an experiment began, and 0.06 moles/liter 25 minutes after the experiment began, what would a linear model look like for a concentration (y) vs. time (x) when predicting the concentration 28 minutes in and when the concentration will go to zero? 
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you have two points (7,0.15) and (25,0.6)
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slope  = (0.60-0.15)/(25-7) = 0.45/18 = 0.025
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Equation Form:
concentration = slope*time + b
You know slope and concentration = 0.6 when time = 25
Solve for "b:
0.6 = 0.025*25 + b
b = -0.025
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Equation:
c = 0.025x - 0.025
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Cheers,
Stan H.