I'll explain u this wid an example...
if u have got 45marks for a total of 60 marks...u need to calculate how much u must have got for 100(i.e. per cent)...
let the % u needto find out be x%
then, x = (100 * 45) / 60
hence x% = 75%
Hope u have understood how to calculate the percentage now....Always remember percentage means per cent i.e the value which we get by dividing wid 100.