How to make unusual let's say equality?

Question

C++ / C#

We have 2 properties. The width of the first object is 1000, the second one is 100.
How can I make them seem to be equal so that the width of the first object depends on the second one. If the width of the second object is equal to 30, then the width of the first object will also adjust to this and if the first object were the second, then it would be equal to 30, but it has a large number. I have seen several programs where everything works according to this principle and I do not understand how it is done, it would seem that two objects differ in volume, but at the same time they are equal and change identically if I drag just one slider, for example. I hope I explained it clearly xD, because the question itself is already something beyond

Answer 1

This is a simple task from the school on the ratio, in this case, of the parties.
Calculate the ratio and change the scale in accordance with it