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SUPPLEMENT for WEBWORK HW03

# SUPPLEMENT for WEBWORK HW03 - Math 135 Supplement for...

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Math 135 Supplement for WebWork HW03 Fall 2010 Prepared by Kellen Myers Several students have inquired about problem 26 from the WebWork. It reads: A bacteria culture initially contains 2500 bacteria and doubles every half hour. With t representing minutes, the formula for the population is p ( t ) = 2500 e kt for some constant k . 1. k = 2. The size of the bacterial population after 60 minutes is . 3. The size of the bacterial population after 9 hours is . Note that the constants (2500, 60, 9) vary from question to question. The general roadblock students come across is this: Compute k by solving: p (30) = 5000 2500 e 30 k = 5000 e 30 k = 2 30 k = ln(2) k = ln(2) / 30 WebWork will accept either “ln(2)/30” or an approximation like “0.231.” This is where things start to go wrong. The next thing the student does is enter the k and t values to compute the second part of this question: p (60) = 2500 e 0 . 231 · 60 This can be plugged right into a calculator to achieve the approximation 9997.05.

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SUPPLEMENT for WEBWORK HW03 - Math 135 Supplement for...

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