Answer:
68.2% of the batteries failed between 17.8 and 20.2 hours.
95.44% of the batteries failed between 16.6 and 21.4 hours.
99.97% of the batteries failed between 15.4 and 22.6 hours.
Step-by-step explanation:
The 68-95-99.7 states that, for a normally distributed sample:
68.26% of the measures are within 1 standard deviation of the sample.
95.44% of the measures are within 2 standard deviations of the sample.
99.97% of the measures are within 3 standard deviations of the sample.
In this problem, we have that:
Mean of 19 hours, standard deviation of 1.2 hours.
About 68.26% of the batteries failed between what two values?
This is within 1 standard deviation of the mean. So 68.2% of the batteries failed between 17.8 and 20.2 hours.
About 95.44% of the batteries failed between what two values?
This is within 2 standard deviations of the mean. So 95.44% of the batteries failed between 16.6 and 21.4 hours.
About 99.97% of the batteries failed between what two values?
This is within 3 standard deviations of the mean. So 99.97% of the batteries failed between 15.4 and 22.6 hours.
