MEDAL AND FAN

The length of time before a type of electric generator breaks down is normally distributed with a mean of 71 months and a standard deviation of 2.5 months. What percent of the generators will break down before 66 months?

16%

2.5%

34%

5%

Question

MEDAL AND FAN

The length of time before a type of electric generator breaks down is normally distributed with a mean of 71 months and a standard deviation of 2.5 months. What percent of the generators will break down before 66 months?
	

16%
	

2.5%
	

34%
	

5%

mrnood · Answer

how many 'standard deviations' is 66 months away from the mean?

You can then use the rule of thumb for 1,2 or 3 SD to get the incidence of breakdowns.