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Interpret change in exponential models: with manipulation

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After a special medicine is introduced into a petri dish full of bacteria, the number of bacteria remaining in the dish decreases rapidly.
The relationship between the elapsed time t, in seconds, and the number of bacteria, B(t), in the petri dish is modeled by the following function:


Complete the following sentence about the rate of change of the bacterial culture. Round your answer to two decimal places.
The bacterial culture loses 12 of its size every
  • Your answer should be
  • an integer, like 6
  • a simplified proper fraction, like 3/5
  • a simplified improper fraction, like 7/4
  • a mixed number, like 1 3/4
  • an exact decimal, like 0.75
  • a multiple of pi, like 12 pi or 2/3 pi