Question

Using the example above as a guide, fill in the missing information. Enter percentage answers to the nearest tenth.

Jim Tree wants to analyze another shipment of Christmas trees based on height. He knows the height of the trees is normally distributed so he can use the standard normal distribution. He measures the height of 500 randomly selected trees in his shipment. Next, he calculates the mean and standard deviation of their heights. The mean is 60 inches and the standard deviation is 12 inches. Now, Jim uses the normal distribution table above to calculate the number of trees in each segment of the distribution.

Standard Deviation | Percentage from table | Number of trees out of 500
-1 to 0 (48 to 60 inches) | 34.1% | ____
0 to +1 (60 to ____ inches) | ____ % | 171
+1 to +2 (72 to 84 inches) | ____ % | ____

Answer 1

first row: -1 to 0 (48 to 60 inches) | 34.1% | ____

they give you the percentage 34.1% and they want the number of trees

so simply calculate 34.1% of 500

Answer 2

I did get that, but what about the rest

Answer 3

row 2:

0 to +1 (60 to ____ inches) | ____ % | 171

if the standard deviation is 12 and the mean is 60, how much is one standard deviation above the mean?

Answer 4

"above" implies addition

so simply add the standard deviation + mean

Answer 5

oh ok, well what about the third row?

Answer 6

the percentage associated with +1 SD to +2 SD is 13.6% so 13.6 would be your percentage, and then you would simply calculate 13.6% of 500

Answer 7

ok thanks!