Studies have shown that people who suffer sudden cardiac arrest have a better chance of survival if a defibrillator shock is administered very soon after cardiac arrest. How is survival rate related to the time between when cardiac arrest occurs and when the defibrillator shock is delivered? This question is addressed in the paper €œImproving Survival from Sudden Cardiac Arrest: The Role of Home Defibrillators€ (by J. K. Stross, University of Michigan, February 2002; available at www.heartstarthome.com). The accompanying data give y = survival rate (percent) and x = mean call-toshock time (minutes) for a cardiac rehabilitation center (in which cardiac arrests occurred while victims were hospitalized and so the call-to-shock time tended to be short) and for four communities of different sizes:

a. Construct a scatterplot for these data. How would you describe the relationship between mean call-to shock time and survival rate?
b. Find the equation of the least-squares line.
c. Use the least-squares line to predict survival rate for a community with a mean call-to-shock time of 10 minutes.

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7912 Mean call-to-shock time, x Survival rate, y 26 90 45 30 5 2