Cross multiplication

Cross multiplication is a way to solve for an unknown number when given two equations. For example, if you have the equations `5x=10` and `x=2`, we can use cross multiplication to figure out what `5` is. To do this, we make the two equations look like a fraction. We do this by flipping the first equation like so: `10/x = 5` and you can then line up the two equations like this: `10/x = 5` and `x = 2`. Now, we can cross multiply. This just means multiplying the two numbers on the ends, like so: `10 x 2 = 20`. That means `5 x 2 = 10`, which is what we started with.