Calculator Skills
Switching Between Fractions and Decimals
One key on most scientific calculators flips an answer between exact fraction and decimal, useful for checking and for matching what the question wants.
Match the form to the question
If the question wants an exact answer, present the fraction or surd; if it wants a decimal to a given accuracy, toggle and round. Being able to see both forms at a keypress also helps you sanity-check an unusual-looking answer.
A worked keystroke sequence with the toggle
- Enter 5 ÷ 8 and press = . Depending on the setting, the display may show 5/8 or 0.625.
- Press the fraction-decimal toggle (often marked S↔D). The answer flips between 5/8 and 0.625 with each press.
- Try 0.375: enter it, press =, then the toggle. It becomes 3/8, its exact fraction.
- Now enter 1 ÷ 3 and press = . The toggle shows the exact fraction 1/3 and the recurring decimal 0.3333…, which never ends.
Let the toggle catch a rounding trap
The toggle is a quick truth-test for exactness. If a value flips cleanly to a simple fraction like 3/8, it is exact and can be written as a fraction.
If it flips to a never-ending decimal such as 0.3333…, then writing 0.33 loses accuracy, and you should keep it as 1/3 unless a decimal is requested. Note that a genuinely irrational number like √2 will not turn into a fraction, the toggle simply leaves it as a surd or a decimal, which is itself a useful signal.
Source:SPM: Format Pentaksiran mulai 2021, Matematik (1449)
Frequently asked questions
Which button switches between a fraction and a decimal?
On most scientific calculators it is a single toggle key, often labelled S↔D. Pressing it flips the current answer between its exact fraction form and its decimal form.
This lets you compute in fractions for accuracy and then convert to a decimal only when the question specifically asks for a decimal answer.
The toggle will not turn my answer into a fraction, is it broken?
No, the number is probably not a simple fraction. Irrational values such as √2 or π have no exact fractional form, so the calculator leaves them as a surd or a decimal.
That is correct behaviour and a useful hint that the answer should stay in surd form or be rounded, not written as a fraction.
Should I answer in fraction or decimal form?
Match whatever the question asks. If it says give your answer to two decimal places, convert with the toggle and round.
If it wants an exact answer, keep the fraction. When the question is silent and the value is a recurring decimal, the fraction is usually the safer, more accurate form to write.