83.33% or if you round it down 83%.
It is best to do these sums on a calculator if possible, as it often involved working with decimal numbers which can be tricky in your head or on paper. To work out the answer to the above sum, you simply work out 5 divided by 6 (basically wherever you see the / sign in math it means divided by) and this will give you 0.83.
You will then need to multiply this by a hundred (since percent means per hundred). To do this you can simply move the decimal point two spaces (one for each of the zeros) to the right. This will give you 83% which is your answer.
Once you understand the process involved which you can then apply to more difficult sums.
To find 1/2 as a percentage (you probably already know that this is a half, and that a half is 50% so this will show you how it works in a sum you know).
1 / 2 (1 divided by 2) = 0.5
0.5 x 100 = 50 %
To find 3/7 as a percentage:
3 / 7 = 0.43
0.43 x 100 = 43%