For example, two voltages, two resistances, two volumes, two lengths etc.

If one value is twice that of the other then we say that they are in the ratio of two to one.

This is written 2:1.

30 volts and 5 volts are in the ratio 30:5 or simplifying 6:1

12 inches and 144 inches are in the ratio 12:144 or simplifying 1:12

3 apples and 4 apples are in the ratio 3:4