Dawnbridge

TI-84 Plus CE field manual for IB Math

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21

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

Open the distribution menu with , then choose 2: normalcdf(.

2

Fill in the wizard: lower -1E99 (a very large negative number standing in for ​−∞; use for the leading sign, then for the E), upper 68, ​μ=60,  ​σ=5.

NORMALFLOATAUTOREALRADIANMP
normalcdf
lower:-1e+99
upper:68
μ:60
σ:5
PasteHelp
3

Choose Paste, then press to evaluate the pasted command.

Result

​P(X<68)≈0.945.

NORMALFLOATAUTOREALRADIANMP
normalcdf(−1E99,68,60,5)
0.9452007083

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).