Question

The mean age at which the population of babies first stand without support is normally distributed with a mean of 13.20 months with a standard deviation of 2.00 months. What is the probability of randomly selecting a sample of 25 children who stood on their own by the average age of 12.2 months or earlier

Answer 1

0.00621

Explanation:

We solve the above question using the

Z score formula. This is given as:

z = (x-μ)/σ/√n

where

x is the raw score = 12.20 or earlier

This means x ≤ 12.20

μ is the population mean = 13.20

σ is the population standard deviation = 2

n is the random number of samples = 25

z = 12.2 - 13.2/2/√25

z = -1/2/5

z = -1/0.4

z = -2.5

Probability value from Z-Table:

P(x≤ 12.2) = 0.0062097

Approximately = 0.00621

Therefore, the probability of randomly selecting a sample of 25 children who stood on their own by the average age of 12.2 months or earlier is 0.00621