Question

The scores on the Wechsler Adult Intelligence Scale are approximately Normal with mean= 100 and standard deviation=15. The shortest interval that covers 90% of WISC scores is closest to...

(80, 129)

(82, 118)

(75, 125)

(73, 119)

(79, 121)

Answer 1

Here

µ = 100

σ = 15

Suppose the interval is (x1,x2)

So are between x1 and x2 =90% = 0.90

So remaining area = 1-0.90 =0.10

So area left to x1 is 0.10 / 2=0.05

and area left to x2 is 0.90 +.05 = 0.95

We will use Ti83/84

Press 2ND...VARS...invNorm

Enter values as

result is

So x1=75

To calculate X2 enter values as

result is

x2=125

So the correct interval is ( 75 , 125 )