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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.
A wave labeled D on a t E coordinate plane, where E is the vertical axis and t is the horizontal axis. The E axis scales by one thousandths. The t axis scales by ones. The wave has a repeating pattern of a large positive spike followed by several small waves centering near the x-axis. The wave starts at the highest point of the spike at (zero, four thousandths). The other highest parts of the wave are at (one, four thousandths), (two, four thousandths), (three, four thousandths), (four, four thousandths), (five, four thousandths), and (six, four thousandths).
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