Question

In a spreadsheet, you can use the function NORM.DIST(upper bound, μ, σ, TRUE) to find the area under a normal curve for values of x less than or equal to a specified upper bound. Suppose the heights of all the children in a state are normally distributed with a mean of 41 inches and a standard deviation of 4 inches. What is the probability that a randomly chosen child is greater than 34 inches tall?

Answer 1

Given Information:

Mean height of children = μ = 41 inches

Standard deviation of height of children = σ = 4 inches

Required Information:

Using Excel find P(x > 34) = ?

Answer:

P(x > 34) = 95.99%

Explanation:

What is Normal Distribution?

We are given a Normal Distribution, which is a continuous probability distribution and is symmetrical around the mean. The shape of this distribution is like a bell curve and most of the data is clustered around the mean. The area under this bell shaped curve represents the probability.  

The Microsoft Excel has a built-in function "NORMDIST" which calculates the probability of a normal distribution.

Syntax:

NORMDIST(x, mean, standard deviation, cumulative flag)  

Where x is the variable of interest

Cumulative flag = TRUE or FALSE

The probability that a randomly chosen child is greater than 34 inches tall is given by

P(x > 34) = 1 - P(x < 34)

Using MS Excel,

P(x > 34) = 1 - NORM.DIST(34,41,4,TRUE)

Which return the probability of

P(x > 34) = 1 - 0.040059

P(x > 34) = 0.959941

P(x > 34) = 95.99%

Therefore, there is 95.99% probability that a randomly chosen child is greater than 34 inches tall.