Answer:99.7%
Step-by-step explanation:
The empirical rule states that for a normal distribution, almost all of the
data will fall within three standard deviations of the mean. It states that
1) 68% of the data falls within one standard deviation of the mean.
2) 95% of the data falls within two standard deviations of the mean.
3) 99.7% of the data falls within three standard deviations of the mean.
From the information given, the mean is $70 and the standard deviation is $9. We want to determine the percentage of her phone bill that is between 43% and 97%
Looking at ±3 standard deviations of the mean, it becomes
70 ± 3×9 = 70 ± 27
The value is between 70 - 27 = 43 and 70 + 27 = 97
Therefore, the percentage of her phone bills that is between 43% and 97% is 99.7%
