I just want to know if I did this correctly or not. This is something I just learned today.

yes I also learnt those today only ..

yes they r correct only

Ratio = Cleaner : Water
                   1     :    3


Find total parts :

Total parts = 1 + 3 = 4


Find 1 part :

4 parts = 1 gallon
1 part = 1/4 gallon


Find 3 parts :

1 part = 1/4 gallon
3 parts = 1/4 x 3
3 parts = 3/4 gallon

Ratio = Cleaner : Water
                   1     :    3
                  1/4   :  3/4


You will need 1/4 gallon of cleaning solution.