If we have an equation (or expression) with variables, we can only solve what it is equal to when we know the variables. The following video will show how to solve an equation when given numbers for the variables.

Video Source (04:13 mins) | Transcript

Simplifying expressions with variables comes in handy a lot when we are given a formula for a certain type of problem. A formula is something that looks like \(pt = a\). This is a formula for finding the amount when we know the percent and the total. We learned about this formula in last week’s lesson on percentages.

In this case, \(p\) represents the percent and \(t\) represents the total. If we were told that the percent was \(75\%\) and the total was \(20\), we could find that the amount was \(15\). This is done by putting our values in for our variables in the formula. \(pt\) becomes \(\lgroup.75\rgroup\lgroup20\rgroup\) which is equal to \(15\), so \(a = 15\).

## Additional Resources

- Khan Academy: Variables, Expressions, & Equations (06:54 mins, Transcript)
- Khan Academy: Evaluating an expression with one variable (01:59 mins, Transcript)

### Practice Problems

**Simplify the following expression to find it's value:**

1. Given that \(d = 3\):

\(7d = ?\) (

\(m − 12 = ?\) (

\(6x + 3 = ?\) (

**As we will explore later, the area of a rectangle can be found by multiplying the length of the rectangle by its width, or \({\text{(L × W)}}\). Use this information to answer the following two questions:**

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