How do you solve simultaneous questions?

When an equation has two or more variables, for example and x and y, more than one equation is need to solve it.  The number of equations needs is equal to the number of variables you have.  For example, if you need to find x and y, 2 equations will be needed. There are multiple ways you can solve simulataneous equations, through substitution, elimination and graphically. Let's consider the first method, substitution.

Here are two example simultaneous equations:

1. x + y  = 13

2)  2x + 5y = 56

Rearranging equation 1 to give x or y explicitly:

3. x = 13 - y

Substituting

3. into 2)

4. 2(13 - y) + 5y = 56

Expand and solve  

26 - 2y + 5y = 56

3y = 30 y = 10

Using equation 3)

x = 13 - y

  = 13 - 10   = 3