How to Use normalcdf on the TI-84 Evo

On the TI-84 Evo, normalcdf is in the DISTR menu: press alpha, then stat, and pick it under Normal. Give it the two ends of a range, the mean and the standard deviation, and it returns the probability that a value falls in that range.

The example here: test scores with a mean of 75 and a standard deviation of 10. What's the probability that a score falls between 85 and 100?

Find the probability between two values

  1. Press alpha, then stat. DISTR is the green label above the stat key, so this opens the distribution menu.
    The TI-84 Evo DISTR menu with 1: Normal highlighted, above Student's t, Chi-Square, Binomial, Geometric, Poisson and Fisher's F
  2. Press enter to open Normal.
  3. Press the down arrow to normalcdf(, then press enter. That opens the Normalcdf setup screen, with a box for each number.
    The Normal menu on the TI-84 Evo with 2: normalcdf( highlighted, between normalpdf( and invNorm(
  4. Type the four numbers, pressing the down arrow after each one. Typing replaces whatever is already in a box.
    • lower is the low end of the range: 85.
    • upper is the high end: 100.
    • μ is the mean: 75.
    • σ is the standard deviation: 10.
    The Normalcdf setup screen on the TI-84 Evo with lower 85, upper 100, mu 75 and sigma 10, and a PASTE button at the bottom
  5. Press zoom. The zoom key works the PASTE button at the bottom of the screen, which puts the finished command on the home screen. Pressing enter here only moves between the boxes.
  6. Press enter. The answer is 0.1524455797, so about 15% of scores fall between 85 and 100.
    The TI-84 Evo home screen showing normalcdf(85,100,75,10) equals 0.1524455797

Greater than or less than one value

The normalcdf command always needs both ends of the range. A "greater than" or "less than" question has no end on one side, so use 1E99 there. That's a 1 followed by 99 zeros, far past any test score. 1E99 is a number so far out on any normal curve that the calculator treats it like infinity.

To type the E, press 2nd, then the comma key (EE is the blue label above it). For −1E99, start with the (−) key.

Probability lower upper Answer
Score above 85 85 1E99 0.1586552596
Score below 85 −1E99 85 0.8413447404

Open normalcdf the same way, type over lower and upper, leave μ at 75 and σ at 10, then press zoom and enter.

The Normalcdf setup screen with lower 85 and upper 1E99, for the probability of a score above 85
The TI-84 Evo home screen with three normalcdf results: 0.1524455797 between 85 and 100, 0.1586552596 above 85, and 0.8413447404 below 85

Good to know

  • The boxes remember your last numbers. Reopen normalcdf and every box still holds what you typed last time, so check all four before you paste.
  • Getting ERROR: SYNTAX? Check for an empty box. A blank upper bound pastes as two commas in a row, and enter gives ERROR: SYNTAX.
  • For z-scores, set μ to 0 and σ to 1. The probability of a z-score between −1 and 1 is normalcdf(−1, 1, 0, 1) = 0.6826894809.
  • Following a video made on another TI-84? Those open the distribution menu with 2nd, vars. On the Evo that opens the MATRIX menu, and DISTR is alpha, stat.
  • Have the probability and need the score? That's invNorm, right below normalcdf in the Normal menu.