Scores on the Wechsler Adult Intelligence Scale are approxim

Scores on the Wechsler Adult Intelligence Scale are approximately Normally distributed with ? = 100 and ? = 12. Please use 2 decimal places to answer the following questions.

Solution

(a)P(X<c)=0.25

--> P((X-mean)/s <(c-100)/12) =0.25

--> P(Z<(c-100)/12) =0.25

--> (c-100)/12=-0.67 (from standard normal table)

So c= 100-0.67*12=91.96

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(b)P(X>c)=0.025

--> P(Z<(c-100)/12)=1-0.025=0.975

--> (c-100)/12 =1.96 (from standard normal table)

So c=100+1.96*12=123.52