According to the Centers for Disease Control CDC 3years old

According to the Centers for Disease Control (CDC), 3years old boys have a mean height of 38 inches and a standard deviation of 2 inches. The distribution is approximately Normal.

a. What percentage of 3-year-old boys have a height of 39inches or more?

b.What percentage of 3-year old boys have aheight of 38 inches or more?

Solution

U = 38
SD = 2

a) x = 39

z = (39 - 38)/2 = 0.5

From the z-table, for z = 0.5, P(x < 39) = 0.6915

So, P(x > 39) = 1 - 0.6915 = 0.3085

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b) x = 38

z = (38 - 38) / 2 = 0

From the z-table, for z = 0 , P(x < 38) = 0.5

So, P(x > 38) = 1 - 0.5 = 0.5