A certain characteristic in a large population has a distribution that is symmetric about the mean m. 80 percent of the distribution lies within one standard deviation d of the mean. If the shelf’s average life is 8.6 years and the standard deviation is 3.4 years, what percent of the distribution has more than 12.0 years as a shelf’s average life?	Choices:	A) 23%	B) 22%	C) 21%	D) 20%	E) 19%
Average = 8.6   SD = 3.4   8.6 - 3.4 &lt; 80% of distribution &lt; 8.6 + 3.4   5.2 &lt; 80% of distribution &lt; 12.0   40% is outside this range.   Given: Distribution is symmetric. So 20% of distribution is less than 5.2 and the other 20% of distribution is greater than 12.0.   Answer: 20%
<result>D</result>
A certain characteristic in a large population has a distribution that is symmetric about the mean m. 80 percent of the distribution lies within one standard deviation d of the mean. If the shelf’s average life is 8.6 years and the standard deviation is 3.4 years, what percent of the distribution has more than 12.0 years as a shelf’s average life?