Every theoretical problem asks for an answer or solution. Trying to find a solution to a problem is known as problem solving. That is, a problem is a gap between an actual and desired situation. The time it takes to solve a problem is a way of measuring complexity. Many problems have no discovered solution and are therefore classified as an open problem.
See also: List of unsolved problems
From the mid 20th century, the field of theoretical computer science has explored the use of computers to solve problems.
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