Dawnbridge

TI-Nspire CX II field manual for IB Math

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22

Normal distribution probabilities

All courses

Use the normal CDF command to calculate probabilities P(a<X<b) from a normal distribution.

Goal

If ​X∼N(60,52), find ​P(X<68).

1

From the Scratchpad calculator, press → 6: Statistics → 5: Distributions → 2: Normal Cdf.

2

Fill in the dialog, moving between fields with : leave the lower bound at -9.E999 (the calculator's stand-in for ​−∞​), upper bound 68, ​μ=60,  ​σ=5. If you ever delete the lower bound, type it back as : the key enters the exponent, giving ​−9×10999.

Scratchpad
RAD
Normal Cdf
Lower Bound:-9.E999▶
Upper Bound:68.▶
μ:60.▶
σ:5.▶
OKCancel
3

Select OK and press . The normCdf( command lands on the calculator page with its value.

Result

​P(X<68)≈0.945.

Scratchpad
RAD
normCdf(−9.E999,68.,60.,5.)
0.945201

Your turn

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

  1. 1

    If ​X∼N(100,152), find ​P(X<120).

  2. 2

    If ​X∼N(50,82), find ​P(X>60).

  3. 3

    If ​X∼N(3.2,0.42), find ​P(3<X<3.9).