How to solve problems involving proportions:

How much lemon juice should be added to 9L water to make a lemonade that is 30% lemon juice?

Step one: Make an equation by reading the question and identifying the components of the equation.

Step two: Simplify the equation by cross-multiplying and moving all the X’s to one side.

Step three: Solve the equation by isolating the X. The answer is 27/7 Litres.