Imagine you are organizing a school concert. The fire regulations state that you can only have 300 people in the hall at any time. People have already set the chairs out, but how many are there? There is an aisle with chairs on either side. The function for the number of chairs is: C = R x A
Where C is the number of chairs, R is the number of rows and A is the number of chairs in an aisle, obtained by adding the number of chairs in the left and right aisles.
Imagine you are going on a long journey and would like to know how much gas you will use and what this will cost. Take a map and see how far you are travelling. For example, a road trip from San Francisco to Los Angeles is about 380 miles. Now find out the fuel economy of your car. To calculate the gas you need use: G = D x E, where G is the quantity of gas in gallons, D is the distance in miles and E is the fuel economy in miles per gallon.
If you know how much gas you will use, you can also calculate how much this will cost. First, find out the price of one gallon of gas (for example, $3) then, use the following function: C = G x P, where C is the total cost, G is the gas needed and P is the price of one gallon of gas.
If you are earning $15 per hour, will this be enough to live off? You know how much your monthly rent is, and how much you spend on food and other expenses. To calculate your monthly income use the following function: I = W x H x D x W, where I is your monthly income, W is your hourly wage, H is the number of hours you work per day, D is the number of days you work per week and W is the number of weeks you work per month.