Respuesta :
Answer:
The inter-decile range of IQ is 40.96.
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 question, we have that:
[tex]\mu = 100, \sigma = 16[/tex]
First decile:
100/10 = 10th percentile, which is X when Z has a pvalue of 0.1. So it is X when Z = -1.28.
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
[tex]-1.28 = \frac{X - 100}{16}[/tex]
[tex]X - 100 = -1.28*16[/tex]
[tex]X = 79.52[/tex]
Ninth decile:
9*(100/10) = 90th percentile, which is X when Z has a pvalue of 0.9. So it is X when Z = 1.28.
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
[tex]1.28 = \frac{X - 100}{16}[/tex]
[tex]X - 100 = 1.28*16[/tex]
[tex]X = 120.48[/tex]
Interdecile range:
120.48 - 79.52 = 40.96
The inter-decile range of IQ is 40.96.
