2). Write an equation and solve. You will not be given credit for your answer if you do not include your equation! This month's cell phone bill was for $15.27 more than last month's cell phone bill. If this month's phone bill is for $72.50, how much was last month's cell phone bill?​

Explanation:

We'll make x the value of last month's phone bill. So if lets say x = 50, this means that last month's phone bill was $50. We don't know yet if x = 50 is the actual solution or not.

We're told that "This month's cell phone bill was for $15.27 more than last month's cell phone bill". This means this month's bill, in terms of x, is x+15.27 dollars. Whatever x is, we add 15.27 onto it getting this month's bill. This works because x is really a placeholder for a number.

Going back to x = 50, that would mean this months bill is x+15.27 = 50+15.27 = 65.27 dollars. We can see that we don't reach 72.50 that we're told the current months bill actually is. Since we don't have a match, this means x = 50 is too small. We can guess and check our way to hopefully land on the answer. However, using algebra is the most efficient method.

The equation we need to solve is:   x+15.27 = 72.50

This is because x+15.27 represents this month's bill and so does the 72.50, as your teacher gave in the instructions.

To solve this equation, we'll undo the "plus 15.27" to isolate x fully. The opposite of addition is subtraction. We'll subtract 15.27 from both sides

x+15.27 = 72.50

x+15.27-15.27 = 72.50-15.27

x = 57.23

Last month's phone bill was $57.23

As a check, adding 15.27 onto last month's bill should get us to 72.50

x+15.27 = 57.23+15.27 = 72.50

It works out, so we've confirmed the answer.

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