35 is what percentage of 50, I'm going to show you with fractions: At the moment it is 35/50 but multiply both sides by 2 and you get: 70/100, multiply it by 100 to get a percentage and you have 70%
You basically just split it right down the middle. if the cost of something is lets say $75.58, then you would divide 75.58 by 2, which is $37.79 hope it helps!!