# 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.