Assume that adults have IQ scores that are normally distributed with a mean of 101.2 and a standard deviation 23.6 Find the first quartile Upper Q 1Q1, which is the IQ score separating the bottom 25% from the top 75%. (Hint: Draw a graph.) The first quartile is
Solution:-
Given that,
mean = = 101.2
standard deviation = = 23.6
Using standard normal table,
The z dist'n First quartile is,
P(Z < z) = 25%
= P(Z < z) = 0.25
= P(Z < -0.67 ) = 0.25
z = -0.67
Using z-score formula,
x = z * +
x = -0.67 * 23.6+101.2
x = 85.388
First quartile =Q1 = 86
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