Question

You are going to mix a gallon bucket of window cleaner. The instructions direct you to mix 1 part cleaner to 3 parts water. How much cleaning solution will you need to use?*

Answer 1

The correct ratio is 1 part cleaner to 3 parts water.

Thus:

Such a solution would have the combined volume 4 parts.

Here we want 1 gallon of cleaning solution, so use 1/4 gallon cleaner and
3/4 gallon water. Note that 1/4 gallon + 3/4 gallon = 1 gallon (as desired),
and that the ratio of cleaning solution volume to water volume is

1/4 cup
------------ = 1:3, as required.
3/4 cup