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Periodicity of algebraic models


A doctor observes the electrical activity of the heart of a patient over a period of time.
The graph below shows the electrical activity, E, in volts, of the patient's heart over time t, measured in seconds. Each spike corresponds to one heart beat.
Approximately how much time is between this patient's heartbeats?
  • 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