Dawnbridge

Casio fx-CG50 field manual for IB Math

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25

Inverse normal

All courses

Use the inverse-normal routine to find the value k with a given cumulative probability P(X<k).

Goal

If ​X∼N(60,52), find ​k​ such that ​P(X<k)=0.9.

1

From the MAIN MENU, open Statistics. If you're already inside another app, press first to get back to MAIN MENU.

2

Press (DIST), then (NORM), then (InvN) to open the inverse-normal wizard.

3

Press (Var) if Data shows List. Set Tail to Left (the probability is to the left of ​k​), then Area = 0.9, ​σ=5,  ​μ=60.

RadNorm2
d/cReal
Inverse Normal
Data:Variable
Tail:Left
Area:0.9
σ:5
μ:60
Save Res:None
↓
CALC
4

Move down to Execute and press .

Result

​k≈66.4.

RadNorm2
d/cReal
Inverse Normal
xInv=66.4077578

Your turn

Work each one on your calculator, then check the answer.

  1. 1

    If ​X∼N(100,152), find ​k​ such that ​P(X<k)=0.95.

  2. 2

    If ​X∼N(24,32), find ​k​ such that ​P(X<k)=0.10.

  3. 3

    If ​X∼N(70,62), find ​k​ such that ​P(X<k)=0.25.