Respuesta :
Answer:
P40 = 77.244
Step-by-step explanation:
Problems of normally distributed samples are solved using the z-score formula.
In a set with mean [tex]\mu[/tex] and standard deviation [tex]\sigma[/tex], the zscore of a measure X is given by:
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
The Z-score measures how many standard deviations the measure is from the mean. After finding the Z-score, we look at the z-score table and find the p-value associated with this z-score. This p-value is the probability that the value of the measure is smaller than X, that is, the percentile of X. Subtracting 1 by the pvalue, we get the probability that the value of the measure is greater than X.
In this problem, we have that:
[tex]\mu = 79.4, \sigma = 8.8[/tex]
What vaule represents P40
This is the 40th percentile, that is, X when Z has a pvalue of 0.4. So X when Z = -0.245.
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
[tex]-0.245 = \frac{X - 79.4}{8.8}[/tex]
[tex]X - 79.4 = -0.245*8.8[/tex]
[tex]X = 77.244[/tex]
P40 = 77.244
