If the cocoa to water ratio for a hot chocolate recipe is 1 tablespoon cocoa to 1⁄4 cup water, how much water do you need if you use 1.5 tablespoons of cocoa?
1/4 cup water / 1 Tsp cocoa = x / 1.5 cocoa cross-multiply
1.5 * 1/4 = 1x
(3/2) (1/4) = x
3/8 cup water = x