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In mathematics, a linear equation is one that contains two variables and can be plotted on a graph as a straight line.
Now we need to look at the graph to see which plan is better if she uses more minutes than that, and which plan is better if she uses fewer.
You can see that the Vendafone plan costs more when she uses more minutes, and the Sellnet plan costs more with fewer minutes.
Since we have 2 types of coins, let's call the number of nickels x and the number of dimes y.
We are given two key pieces of information to make our equations: the number of coins and their value.
We may be considering a purchase—for example, trying to decide whether it's cheaper to buy an item online where you pay shipping or at the store where you do not.
Solving Problems Using Linear Equations
Or you may wish to join a CD music club, but aren't sure if you would really save any money by buying a new CD every month in that way. The first plan, with Vendafone, costs per month, with calls costing an additional 25 cents per minute.
Or you might be considering two different phone contracts. The second company, Sellnet, charges per month, but calls cost only 8 cents per minute. You should see that Anne's choice will depend upon how many minutes of calls she expects to use each month.
We start by writing two equations for the cost in dollars in terms of the minutes used.
The first trick in problems like this is to figure out what we want to know.
This will help us decide what variables (unknowns) to use.