What are real numbers? how are real used to solve problems

Real numbers are all numbers that you can get as a solution to a question.
Basically all numbers are real numbers if you can do whatever you want with it and get it as the answer.
I know this sounds like all numbers but there are number which dot not have solutions like square root of a minus number.For example of you type in root of -25 it will give you error

the law of definite proportions states samples of a compound will always contain the same proportion of elements by mass. in other words, a given compound will always contain the same elements in the same proportions by mass.the law of multiple proportions states when two elements combine with each other to form more than one compound, then the weights of one element that combine with a fixed weight of the other are in a ratio of small whole numbers.