Analytical methods are typically only solvable in cases of “simple” models. Numerical methods, in contrast, provide ways to manipulate complex math problems so that they may be solved by simple processes. These methods allow for imperfect and complex models to be approximated, usually with great accuracy.  Numerical methods can account for more variables and dimensions than would be solvable when using analytical methods.

Note that the numerical solution is an approximation.  In most cases it will be close enough, which is fine for most engineering problems.  Typically mathematicians have more time and funding to find an analytical solution, but the demands of business usually necessitates an approximate solution for engineers working in industry.

Source:http://www.crosscuttingconcepts.com/stem-articles/31-an-introduction-to-numerical-methods