Answer:
Rhoda, whose ACT has a z-score of 1, scored in the 84th percentile in the ACT, compared to Bill, whose SAT has a z-score of -2, who scored in the 2nd percentile on the SAT. Due to the higher percentile(higher z-score) on her test, Rhoda did better on her respective test than Bill, and thus, his logic is wrong.
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.
Bill:
Scored 300, so
SAT has a μ of 500 and a σ of 100.
His z-score is:
has a p-value of 0.02.
This means that Bill, whose SAT score has Z = -2, scored in the 2nd percentile.
Rhoda
Scored 25, so
.
ACT has a μ of 20 and a σ of 5
Her z-score:
has a p-value of 0.84
This means that Rhoda, whose ACT score has Z = 1, scored in the 84th percentile.
What is wrong with Bill’s logic ?
Rhoda, whose ACT has a z-score of 1, scored in the 84th percentile in the ACT, compared to Bill, whose SAT has a z-score of -2, who scored in the 2nd percentile on the SAT. Due to the higher percentile(higher z-score) on her test, Rhoda did better on her respective test than Bill, and thus, his logic is wrong.