Step-by-step explanation: If we use the variable <em>p </em>to represent our pizzas and <em>s</em> to represent our sodas, if our first equation states than 8 slices of pizza and 5 sodas cost $36.50, that's 8p + 5s = 3650.
Notice that I expressed cost in terms of cents so
that we can avoid having to deal with decimals.
In our second equation, 4 slices of pizza and
10 sodas cost $37, that's 4p + 10s = 3700.
Now let's rewrite our two equations on top of one another.
8p + 5s = 3650
4p + 10s = 3700
To solve this system of equations, I would use addition.
I would multiply the bottom equation by -2
to create a situation where our p's will cancel.
When we do that, we get -8p - 20s = -7400.
Now rewrite the equations once again ~
8p + 5s = 3650
-8p - 20s = -7400
Now add the equations together.
So we have -15s = -3,750.
Divide both sides by -15 and s = 250.
Remember that I expressed cost in terms of cents so
since s = 250, it really means that a soda is $2.50.
Now just plug an s back in for the s in one equation.
When we do this, we find that p = 300.
So a pizza is $3.00
