The reason why this is true is because if a milkshake is one whole, or one hundred percent, it means that to find the percentage of banana we have to find how many percents add up to one whole part. To to this we have to see how many parts we have in the given ratio. The 4 parts of milk, 2 parts of banana and one part of protein powder mean that the whole milkshake has 7 parts and the banana makes up for 2/7 of the whole or in percents: (100/7)*2=14.285*2=28.571%
