Maple tree diameters in a forest area are normally distributed with mean 10 inches and standard deviation 2.2 inches. Find the proportion of trees having a diameter less than 9 inches.
The formula for calculating a z-score is z = (x-μ)/σ
where x is the raw score
μ is the population mean
σ is the population standard deviation
z = (9 - 10)/2.2
z = -1/2.2
= -0.45455
Probability value from Z-Table:
P(x ≤ 9) = P(x < 9)
= 0.32472
Therefore, the proportion of trees having a diameter less than 9 inches is
