Arecipe for pastry has flour, butter and water mixed in the ratio 24 : 8 : 3 if fiona follows the recipe and uses 3 cups of flour, how many cups of butter should she use?

To determine the amount of butter in cups that is required to prepare the recipe given the amount of the flour supplied, we calculate first for the ratio of the flour by the amount of butter.

Ratio = amount of flour / amount of butter
Ratio = 24 / 3 = 8

This means that there is 8 cups of flour in every cup of butter.

Amount of butter = (3 cups of flour) x (1 cup of butter / 8 cups of flour)
Amount of butter = 3/8 cups of butter

Hence, the amount of butter needed is 3/8 cups. 

The same can be done in order to determine the amount of water needed to be mixed for the recipe.