How do I solve simultaneous equations?

A easy way to solve simultaneous equations is to substitiute one equation into another and then equate to find one of the unknowns. Once this has been found its a simple matter of substituting it back into the original equation to find the other unknown,

Example: Solve 2a+3b=13 & a+5b=17

Rearrange "a+5b=17" so a=17-5b. Then reintroduce this into equation 1.

 2(17-5b)+3b=13 Solving gives b=3

Substituting b=3 into a+5(3)=17 and solving gives a=2