Mary mixes white paint and blue paint in the ratio 2:3 she makes a total of 20 litres of paint how much more blue paint does she need to add to the mix ture so that the ratio of white paint to blue paint becomes 1:7

There's currently 20 liters of paint that's 2 parts white and 3 parts blue.

This tells us that there is 8 liters of white and 12 liters of blue.

We need paint that's 1 part white and 7 parts blue.

Which means we need 8 liters of white and 8 (7) liters of blue.

This amounts to a total of 56 liters of blue.

We already have 12, so we need to add an additional 44 liters of blue paint.