Mental math can be used to find a product.

Trying to simply equations as much as you can is the only thing that will help you do the mental mathematics.For example, in the first equation.

You wouldn't want to use 25 by 87 in the next one, so we'll use 4 to get 100 and then use 100 by 86 to reach 8700.

The precedence of each of the equations can be changed by using parenthesis and other punctuations.

The ability to do moderately complicated calculations in any order is what you need, but you must respect any brackets that you see.

Technical names are given to these properties.The properties only apply to + and x operations.