Ratio shows the relationship between two or three numbers, for instance, how many times the first or the second number can enter the third number. Example, 3:2:1 is twice 6:4:2. Proportion on the other hand, refers to two variables(let's say a number)that has a constant ratio.For instance, y= kx, here k is the constant value that will equalise both parties,( the y and the x value).
On the other hand, unitary method means the use of necessary calculations to find the desired answer related to variations. In short, unitary methods involve the use of ratios and proportions to find the desired value.