The ratio of red to blue in purple dye is 2: 3 how many parts of blue need to be added to change the dye to 80% blue ?

Add the two numbers in your ratio and divid if from one hundred
This would equal 20
So to find the percentage for the colours as they are time the two ratio number to get 40:60 this is also the percentages.

If you add five more blue parts in to the ratio and leave the red alone you will get 2:8 this would give you a 80% blue part.

So the answer is
5 parts of blue are needed to make the mixture 80% blue.