Answer:
Samantha's grade was 1.29 standard deviations above the class mean, that is, she scored better than 0.9015 = 90.15% of the class.
Step-by-step explanation:
Z-score:
In a set with mean and standard deviation
, the z-score of a measure X is given by:
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 p-value, we get the probability that the value of the measure is greater than X.
In this question:
She scored better a proportion of the class given by the p-value of z = 1.29
z = 1.29 has a p-value of 0.9015.
Samantha's grade was 1.29 standard deviations above the class mean, that is, she scored better than 0.9015 = 90.15% of the class.