normal distribution, mean = 80 and standard deviation = 5. score? separates the top 10% of the scores from the lowest 90% of the scores

Asked Oct 28 '17 at 18:18

Active Oct 28 '17 at 18:18

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Checking my work: M = 80 SD = 5 X = ? scored 90% better than others. Closest area from table was .8997 giving a z-score of 1.28.

using the formula z = (x - M)/SD, my answer is 86.4

asked Oct 28 '17 at 18:18

S. Smith

Seems to be good! The $z$-value is correct as I calculated with PARI/GP and you also normalized the variable. – Peter Oct 28 '17 at 18:21
I agree it seems right (+1). You used the normal table properly. In R statistical software: The statement qnorm(.9, 80, 5) returns 86.40776. – BruceET Nov 05 '17 at 02:14

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