How to Enter Fractions on a TI-84

Fractions cause more wasted time on a TI-84 than almost anything else, and the reason is nearly always the same: the decimal point gets used where a fraction template belongs. The calculator has two separate tools for fractions, and they do different jobs. One enters a fraction exactly, and the other converts a number that is already on the screen.

It is worth knowing which situation you are in before you start pressing keys. If you are copying a question that already contains a fraction, you want the template. If you have just done a division and the answer arrived as a decimal, you want the conversion.

The two tools at a glance

On the TI-84 Plus, the label n/d is printed above the Y= key, which is the shortcut to remember. On the CE the same menu opens with the same two keys.

Method 1: the n/d fraction template

Pressing ALPHA and then Y= opens the FRAC menu.

Choose 1: n/d and a small two-box fraction template appears with the cursor in the upper box. Type the numerator, press the down arrow, type the denominator and press ENTER. In MathPrint mode the result is drawn as a stacked fraction; in Classic mode you get the same mathematics with a heavy fraction bar.

Suppose you need to add three eighths and one quarter. Enter 3/8 through the template, press the plus key, enter 1/4 through the template again, and press ENTER.

The display never becomes a decimal, because the calculator is holding two whole numbers and a ratio rather than one approximate value. That is the property you want when a question says “give your answer as a fraction”.

For measurements and mixed numbers, 2: Un/d builds the same template with a whole-number box in front, so seven quarters can be entered as 1 and 3 over 4. The FRAC menu also offers 4: ▶n/d◀▶Un/d to convert between the improper and mixed forms of an answer you already have.

Method 2: converting a decimal with MATH ▸ 1:▶Frac

The second method starts with a number already on screen, usually an answer from a division. Press MATH, choose 1:▶Frac and press ENTER. The new line shows the same value written as a fraction.

The same command works on a whole expression rather than a single number, and it works on the previous answer through 2nd ANS, so you can finish a long calculation and then convert the result without retyping any of it.

There is a limit to be aware of. ▶Frac looks for a simple fraction that fits the number it has been given. It will happily turn 0.375 into three eighths, but if you ask it to convert something irrational such as the decimal form of the square root of two, no reasonable fraction matches and the calculator simply returns the decimal. That failure is information: it tells you the value has no short fractional form.

Why a decimal you type is only an approximation

This is the part that costs marks. When you enter a fraction through the n/d template, the calculator stores the numerator and the denominator as whole numbers. The value one third stays as one over three, and any arithmetic you do with it keeps that exactness for as long as the numbers stay manageable.

When you type 0.333333333 instead, you have entered a different kind of object: a decimal held in the calculator’s floating-point format. Most decimals cannot be represented exactly that way, so what is stored is the closest value the calculator can manage. It looks like a third on screen, but it is not a third, and the difference shows up the moment you multiply it back by three or ask for an exact answer.

The practical rule is simple to remember. When a question expects an exact answer, enter fractions with the template. Use the decimal point only when a decimal is what the question asks for, or when the number is genuinely a measurement rather than a ratio.

Fractions in the Y= editor, the table and answers

The template is not confined to the home screen. You can put a fraction directly into the Y= editor, for example entering Y1 = 3/8 X + 1 with the template, and the calculator graphs the exact line rather than a line drawn from a rounded decimal. Fractions entered this way also display as fractions in the TABLE, which makes them easier to check against your own working. If you want to test such a line against a graph, see our guide to finding intercepts.

One thing to watch: a fraction template left half empty, or an expression with an unbalanced bracket around it, will stop the calculator evaluating the line. The usual symptom is ERR: SYNTAX, and pressing 2:Goto on the error screen takes the cursor straight to the character the calculator objected to, which is normally the empty box in the template.

Fractions on exam day

Fraction answers are one of the places where a correct method can still lose marks, because a displayed decimal is not a displayed fraction. Practising the template until the keystrokes are automatic is worth more than any calculation shortcut.

Both the SAT and the ACT permit a graphing calculator such as the TI-84 on the sections where calculators are allowed, while calculators with a computer algebra system are prohibited. Neither board will read a rounded decimal as a fraction for you, so check the form each question asks for. See our SAT calculator policy and ACT calculator policy pages for the rules in force, and confirm the current wording with the board before test day.