The class scores of a history test have a normal distribution with a mean mu is equal to 79 and a standard deviation sigma is equal to 7 If Opal’s test score was 72 , which expression would she write to find the z -score of her test score?
Answer
A
z is equal to the fraction with numerator 72 minus 79 and denominator 7
B
z is equal to the fraction with numerator 72 minus 7 and denominator 7
C
z is equal to the fraction with numerator 79 minus 72 and denominator 7
D
z is equal to the fraction with numerator 7 minus 79 and denominator 7
Explanation
Use the z-score formula z = (score − mean) / standard deviation. Substituting Opal’s score of 72, the mean of 79, and the standard deviation of 7 gives z = (72 − 79) / 7. This is choice A, and it gives a negative z-score because her score is below the mean.
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