One way to solve a problem.

A person will try something, get it wrong, learn from the mistakes, try again, and hopefully eventually get it right.

Many great ideas and inventions were devised through the process of trial and error.

"allow it" means to just leave something alone, or don't worry about it. People in West London say this quite often.

This is a term you would expect when not completing your senior school mathematics. Although there is that rare occasion where your teacher does not know how to teacher and tells you to pretty much go ahead and yolo the shit out of your exams.

The next best thing to guessing

trying something untill you get it right

The story of my life.

A systematic means of determining a solution to a problem, often involving a large amount of time; often involves eliminating possibilities.