Ian's Tree Farm grows spruce trees for plant nurseries. The average annual increase in tree diameter is 7.9 centimetres with a standard deviation of 1.3 centimetres. A random sample of n = 50 trees is collected. What is the probability of the sample mean being less the 7.4 centimetres?
A) 0.0033
B) 0.4977
C) 0.5023
D) 0.9977
E) 0.9954

Question

Quizplus · Accepted Answer

The standard error of the mean is 1.3/sqrt(50). The z-score for 7.4 is (7.4-7.9)/(1.3/sqrt(50)), which is approximately -2.72. The probability of a z-score being less than -2.72 is about 0.0033.

Ian's Tree Farm Grows Spruce Trees for Plant Nurseries