Numi is a calculator app that allows to describe tasks the natural way and instantly get an accurate answer. For example, $20 in euro - 5% discount or today + 2 weeks.
To use workflow make sure Numi installed and running. Prefix your calculations with 'n', for example,'n (20% of 45)/12', 'n $20 in Euro' or 'n time in Tokyo'. Also, note, only development version supports Alfred workflow ATM, please download it at http://numi.io/static/dev/Numi.zip