You can have a calculator add these numbers for you. Most will report the result as a decimal. There are fraction calculators on-line, if your graphing calculator does not have a fraction display mode.
If you want minutes, multiply the fraction (or decimal) by 60 minutes.
So the question here is just simply what percentage is 10 out of 50 correct? You would basically just do 10/50 times 100 which will give you 20 percent as your answer.