# What's the proper way to do percent multiplication in Mathematica? [closed]

I'm very new to Mathematica and I want to calculate percent multiplications. See below image. In In[3], I pressed space after 50% and then pressed 80%. Mathematica automatically added the multiplication sign. In In[4], I manually pressed *, the multiplication sign. Both seem not work. Where is the problem? Thanks.

• % represents the last output. See Out in documentation.
– Kuba
Sep 10, 2019 at 16:16
• If you hate yourself, you can wrap everything with quantities: Quantity[50, "Percent"]*Quantity[80, "Percent"] means 50%*80%. The output will be 2/5 (not in percent), so not really useful. Why don't just use standard fractions instead, and multiply the result by 100 at the end to check the percentage? Sep 10, 2019 at 16:20
• You could define your own symbol, e.g., ¢ = 0.01. Sep 10, 2019 at 18:32
• @MichaelE2 - Rather than always use machine precision, I believe an exact value would be better, i.e., ¢ = 1/100. At the end, machine precision can be coerced using N if desired. Sep 10, 2019 at 18:41
• @BobHanlon That was my first choice, but then I thought better of it. I cannot recall ever being interested in exact percentages. I'd say use tool that does what you want. Sep 10, 2019 at 19:58

## 1 Answer

The percent symbol % in Mathematica represents the last output Out[-1], see the Documentation for Out. Hence the results you observe.

In principle you can use Inline Free-form Input for this: press Ctrl+= and type your 50%, then press , * and Ctrl+= again and type your next percent quantity 80%, and so on:

Then press Shift+Enter to perform the computation:

59/100


Alternatively you can take the suggestion by Michael E2 and define your own percent symbol like ¢ = 0.01 and then type 50¢ instead of 50% with similar effect:

The symbol ¢ (\[Cent]) has built-in alias EsccentEsc. So there are two ways to type it in the FrontEnd: as \[Cent] or as EsccentEsc. It is also possible to define a keyboard shortcut for it using one of the methods described here:

• I get the cent sign with the option key plus "4" but that may vary. Sep 11, 2019 at 10:28
• @MichaelE2 On my system (Win7) Alt+4 is a shortcut for the "Section" style. Sep 11, 2019 at 10:31