Some calculators can show a decimal as a fraction if applicable. eg. 1.333333 -> 1r1r3 on my calculator (hardware) representing \$1 \frac{1}{3}\$. Can the built in calculator do that? If not which (software) can?
* Whats wrong with my math?
You might be able to use Wolfram Alpha as an web application in a few days with 11.10. http://www.webupd8.org/2011/10/install-epiphany-320-with-web.html With 11.10 you can install epiphany and have Wolfram Alpha as a web application and have it saved as an launch-able icon in Unity. Hope this helps.
What are your constraints? Are you allowed to use online calculators? If so, just use Wolfram Alpha or one of the shortcuts to it.
A search reveals Qalculate, but it's a little... pink, for my taste. Perhaps it can be themed. Also, it requires the Qt library, so expect a lot of things to be installed for just this simple program if you don't have other Qt-dependent programs already on your computer.
Giving below link to a bash script to do the above said http://advantage-bash.blogspot.in/2012/03/convert-decimal-to-fraction.html