How to get the percentage of a number in an interval?

Question

Mathematics

Goodnight. For a long time I suffer, I seem to get along around the bush, but I can’t solve the problem in any way.
I don’t know how to correctly describe the task, so I’ll try with examples.
There is an interval: 40 - 60
There is a number: 50
What percentage is this number in the given interval?
In fact, it can be seen that the number is in the middle between 40 and 60, that is, the result will be 50%. But by what formula to get this result - I do not understand.

Answer 1

For convenience, shift the boundaries and the value to 0
60 - 40 = 20
50 - 40 = 10
Then calculate the percentage of the number from the upper limit 10/20 * 100% = 50%