Math CentralQuandaries & Queries


Question from Shaneka, a student:



I am going to try a different problem.

Solve for r if 5r - 8 = 17

You can think of the equation as a balance with the equal sign at the balance point and equal amounts on either side so that the balance doesn't tip. You want to manipulate what is on both sides, always maintaining the balance and end with an equation of the form

r = some number.

First I want to remove the -8 from the left side of the equation. I can do this and maintain the balance (equality) by adding 8 to each side. Thus

5r - 8 = 17
5r - 8 + 8 = 17 + 8
5r = 25

I am almost there. Divide both sides by 5. This maintains the equality and gives

5r = 25
5r/5 = 25/5
r = 5

Now try your equation.

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