InvNorm on Casio Calculators

Last reviewed: June 2026 by the InvNorm Calculator Editorial Team. Report an issue

Casio graphing calculators include an inverse normal distribution function that works similarly to the TI-84's invNorm. However, the menu navigation and labeling differ across Casio models. This guide covers the most common Casio graphing calculators and walks through examples so you can confidently find inverse normal values on your device.

Supported Casio Models

The inverse normal function (InvN or InvNorm) is available on these Casio calculator families:

• fx-9750GIII / fx-9860GII / fx-9860GIII — monochrome graphing calculators widely used in classrooms.
• fx-CG20 / fx-CG50 — color graphing calculators (PRIZM series) with a high-resolution display.
• ClassPad II (fx-CP400) / ClassPad 330 — touch-screen CAS calculators with a different menu system.

Basic scientific calculators such as the fx-991EX or fx-82 series do not include distribution functions.

Navigation on the fx-9860 Series

Follow these steps on an fx-9860GII, fx-9860GIII, or fx-9750GIII:

1. From the main menu, select the STAT icon (or press the number key corresponding to Statistics).
2. If prompted, you can enter or select a data list. For distribution calculations, you do not need data in the list.
3. Press F5 (DIST) to open the distribution menu.
4. Select F1 (NORM) for normal distribution functions.
5. Select F3 (InvN) to access the inverse normal function.

The calculator now prompts you for input. Depending on the OS version, you may see a Tail selector that lets you choose Left, Right, or Central. Enter the area (probability), the standard deviation (σ), and the mean (μ).

Input Fields

• Tail: Select Left (for left cumulative probability), Right (for right tail probability), or Central (for the area in the center of the distribution).
• Area: The probability value (between 0 and 1).
• σ (sigma): Standard deviation. Enter 1 for the standard normal distribution.
• μ (mu): Mean. Enter 0 for the standard normal distribution.

Press EXE to calculate. The result appears on screen.

Navigation on the fx-CG50 (PRIZM)

The fx-CG50 follows the same general path as the fx-9860 series, but the color screen makes menu options easier to read:

1. From the main menu, select Statistics.
2. Press F5 (DIST) or navigate to the Distribution submenu.
3. Select F1 (NORM) → F3 (InvN).
4. Fill in Tail, Area, σ, and μ.
5. Press EXE to see the result.

The fx-CG50 supports the tail selector, making it straightforward to work with right tail and central area problems without manual conversions.

Navigation on the ClassPad

On ClassPad models (ClassPad 330, ClassPad II fx-CP400):

1. Open the Main application or Statistics application.
2. Tap the Calc menu → Distribution.
3. Select Inverse Normal from the list of distributions.
4. Enter the tail setting, area, σ, and μ.
5. Tap OK or press EXE.

The ClassPad's touch interface makes it easy to navigate. Some ClassPad models also allow you to type InvNormCD or InvNorm directly in the command line of the Main application.

Example 1: Left Tail on a Casio

Problem: Find the Z score corresponding to the 95th percentile of the standard normal distribution.

1. Navigate to InvN (STAT → DIST → NORM → InvN).
2. Set Tail to Left.
3. Enter Area: 0.95
4. Enter σ: 1
5. Enter μ: 0
6. Press EXE.

The calculator displays approximately 1.6449. This is the Z score where 95% of the distribution lies to the left.

Try this example in the calculator

Example 2: Right Tail on a Casio

Problem: Lightbulb lifetimes are normally distributed with μ = 800 hours and σ = 40 hours. Find the lifetime exceeded by only 10% of bulbs.

If your Casio has a tail selector, set it to Right and enter Area = 0.10. If your model does not have a tail selector, use the left cumulative probability: 1 − 0.10 = 0.90.

1. Tail: Right (or use area 0.90 with Left)
2. Area: 0.10
3. σ: 40
4. μ: 800
5. Press EXE.

Result: approximately 851.26 hours. About 10% of lightbulbs last longer than 851 hours.

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Example 3: Central Area

Problem: Find the Z scores that enclose the central 99% of the standard normal distribution.

1. Set Tail to Central.
2. Area: 0.99
3. σ: 1, μ: 0
4. Press EXE.

The calculator returns lower boundary approximately −2.5758 and upper boundary approximately 2.5758.

Try this example in the calculator

Differences Between Casio Models

Tips for Casio Users

• If you cannot find the DIST menu, make sure you are in the STAT application, not the Run-Matrix application. Some models require you to be in Statistics mode.
• The Casio tail selector is a significant advantage over the TI-84, which always requires left cumulative probability. Use the tail selector to avoid manual conversions.
• If your result looks wrong, double-check that σ and μ are entered in the correct order. Some older Casio firmware displays σ before μ, which is opposite to the TI-84 convention of (μ, σ).
• Remember that the probability (area) must be between 0 and 1 exclusive. Entering 0 or 1 will produce an error.

Frequently Asked Questions

Related Calculators

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