Final answer:
Using the 68-95-99.7 rule for normally distributed data, the relative frequency of rates greater than 90 is 2.35%, assuming 90 is above two standard deviations from the mean.
Step-by-step explanation:
The question involves using the 68−95−99.7 rule, also known as the empirical rule, which applies to normally distributed data. According to this rule, approximately 68% of data falls within one standard deviation of the mean, 95% within two standard deviations, and 99.7% within three standard deviations.
When looking for the relative frequency of rates greater than 90, we're interested in the percentage of data that falls above a certain value. If we assume that 90 represents a value above one standard deviation from the mean, then we'd expect about 16% (half of 32%, since one standard deviation on either side of the mean accounts for 68%) of the data to fall above this. If 90 represents a value above two standard deviations from the mean, 2.35% of the data would fall above this according to the empirical rule (100% - 97.65%, where 97.65% represents the percentage within two standard deviations). Therefore, the correct answer would be b) 2.35%. This is because the relative frequency of rates greater than a particular value is the same as looking for the percentage of data falling outside a certain threshold on the higher side of the normal distribution.