Get exact fractions and surds instead of long decimals, or convert a decimal answer back to a tidy fraction to check it.
In short: Fraction mode makes the calculator display results such as 3/4 instead of long decimals, and on some models it also shows exact values such as surds. It is set in the mode or settings menu, and a fraction key can convert a decimal. Use it when a question asks for an exact answer, and give decimals only when required.
| TI-84 Plus CE | Casio fx-CG50 and fx-CG100 | TI-Nspire CX | |
|---|---|---|---|
| Key sequence | After a calculation press MATH → 1:▶Frac then ENTER to turn the last answer into a fraction. | Press the F↔D key to toggle the answer between fraction and decimal; Math input mode (SET UP) shows surds and stacked fractions. | Press ctrl → ENTER (instead of ENTER) for the exact form; or menu → Number → Approximate to Fraction. |
Tip: Convert to a decimal only at the very end - keep exact values through the working.
Tip: Convert to a decimal only at the very end - keep exact values through the working.
Tip: Convert to a decimal only at the very end - keep exact values through the working.
Here's a real IB-style question that uses exactly this technique.
A calculation gives 0.875. Write this as an exact fraction.
Get exact fractions and surds instead of long decimals, or convert a decimal answer back to a tidy fraction to check it. A mark scheme asks for an exact answer, not a rounded decimal. Checking whether a decimal you've calculated is really a tidy fraction or surd.
1. After a calculation press MATH → 1:▶Frac then ENTER to turn the last answer into a fraction. 2. Use this to confirm a messy decimal is really a nice value like 7/8 or √2.
1. Press the F↔D key to toggle the answer between fraction and decimal; Math input mode (SET UP) shows surds and stacked fractions. 2. Use this to confirm a messy decimal is really a nice value like 7/8 or √2.
1. Press ctrl → ENTER (instead of ENTER) for the exact form; or menu → Number → Approximate to Fraction. 2. Use this to confirm a messy decimal is really a nice value like 7/8 or √2.
Convert to a decimal only at the very end - keep exact values through the working.
In the worked example on this page (1 mark, Paper 1), the marks are: A1: 7/8.
Questions that need this technique link back to this guide. Try one in practice mode, or see every GDC guide.