Problem solving consists of using generic or ad hoc methods, in an orderly manner, for finding solutions to problems. Some of the problem-solving techniques developed and used in artificial intelligence , computer science , engineering , mathematics , or medicine are related to mental problem-solving techniques studied in psychology.
Considered the most complex of all intellectual functions, problem solving has been defined as a higher-order cognitive process that requires the modulation and control of more routine or fundamental skills.  Problem solving has two major domains: mathematical problem solving and personal problem solving where, in the second, some difficulty or barrier is encountered. 
In mathematics and computer programming , the order of operations (or operator precedence ) is a collection of rules that reflect conventions about which procedures to perform first in order to evaluate a given mathematical expression.
Since the introduction of modern algebraic notation, multiplication has taken precedence over addition.   Thus 3 + 4 × 5 = 4 × 5 + 3 = 23.
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You can't simplify an expression without fully understanding the order of operation! Follow along with this tutorial to see how to use the order of operations to simplify an expression.
To add numbers, you can line up the numbers vertically and then add the matching places together. This tutorial shows you how to add numbers vertically!