Normal Distribution Curve Question

Question

If a normal distribution curve has a mean of 20.3 and a standard deviation of 4.3, how would you find the points for the first and third quartiles?

Answer 1

Get a z-score table:

https://www.stat.tamu.edu/~lzhou/stat302/standardnormaltable.pdf.

 

The first quartile is at 0.2500. This is between a z-score of -0.67 and -0.68.

You can extrapolate to find the exact number.

 

The third quartile is at 0.5000. This is the mean.

 

To find the z-score for the first quartile, substitute the number you determined above into the formula

 

z = (X - μ) / σ, where X = data number, μ = mean, σ = standard deviation.