Sam ple Test Problems Pa ge | 11 42. Scores on the Wechsler Adult Intelligence S

Question

Sam ple Test Problems Pa ge | 11 42. Scores on the Wechsler Adult Intelligence Scale for the 20-34 age group are normally distributed with -110 and 25 a. What percent of people in this age group have scores above 110? b. What percent have scores above 160? C. In what range do the middle 80% of all scores lie- d. Find the 95th percentile and interpret its meanings. 43. A large college class has 800 students, broken down into section meetings with 40 students each. On the final exam, scores followed a normal distribution with a mean of 72 and a

Explanation / Answer

42) for normal distribtion:z score =(X-mean)/std deviation

hence a) % of people scores above110 =P(X>!10) =1-P(X<110) =1-P(Z<(110-110)/25) =1-P(Z<0)=1-0.5 =0.5~ 50%

b)

% of people scores above160 =P(X>!60) =1-P(X<160) =1-P(Z<(160-110)/25) =1-P(Z<2)

=1-0.9925=0.02275~2.28%

c)

for middle 80% CI ; critical z =-/+ 1.28

hence rane of values =mean -/+ z*std deviation =110 -/+ 1.28*25 =77.96 to 142.04

d)

for 95th percentile ; z =1.6449

therefore corresponding value =mean+ z*std deviation =110+1.6449*25 =151.12

that means that 95 percentage of people have Wechsler Adult Intelligent scale score less then 151.12 and 5 percentage of people have score above 151.12/

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