# Evaluating a Formula

A **math formula** is an equation that describes the relationship between two or more variables.

When you **evaluate **a formula, you substitute certain variables with given values and solve for any unknown variable.

For **example **, the formula for calculating the number of gallons of gasoline (n) purchased,

is given by n = $\frac{C}{p}$, where C is the total cost of the gasoline purchased and p is the price per gallon.

Evaluate the formula n = $\frac{C}{p}$, to find the number of gallons of gasoline, given that the total cost is $ 75 and the price per gallon is $ 3.98

### Solution

**Step 1:**

The number of gallons’ n is found by replacing the variables C and p with $ 75 and $ 3.98 in given formula

**Step 2:**

n = $\frac{C}{p}$ = $\frac{75}{3.98}$ = 18.8 gallons

**Step 3:**

So, n = 18.8 gallons

Evaluate speed of a car from the formula s = $\frac{D}{t}$, given that the distance traveled D is 150 km in time t = 2 hours.

### Solution

**Step 1:**

Given D = 150 km; time t = 2 hours

**Step 2:**

Speed s = $\frac{D}{t}$ = $\frac{150}{2}$ = 75 km per hour.

**Step 3:**

So, Speed s = 75 km per hour.