In a mixture of alcohol and water the concentration of alcohol is 55%. Water is 20 ml less than alcohol in the mixture. There should be _____ ml of alcohol and ____ ml of water to make up ____ ml of mixture

Think on it. If there were 55 ml alcohol, there would be 45 ml water.

That's 10 ml less. We have 20 ml less, so there must be

110 ml alcohol
90 ml water