(a) The empirical rule for the normal distribution states that approximately 95% of the data points lie within the range plus and minus 2 standard deviations of the population mean. Therefore one standard deviation can be found as follows: $\sigma=\frac{70-22}{4}=?$ (b) Firstly find the z-score for 25 beats per minute as follows: $Z=\frac{25-45}{\sigma}=?$ The use a standard normal distribution table to find the required probability.