SOLUTION: If 9 is added to twice a number and this sum is multiplied by 3, the result is the same as if the number is multiplied by 4 and 13 is added to the product. What is the number?

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Question 833: If 9 is added to twice a number and this sum is multiplied by 3, the result is the same as if the number is multiplied by 4 and 13 is added to the product. What is the number?
I got a -7. But when I plugged the -7 back into the equation, it didn't work. What am I doing wrong?
Thank you.
Answer by arden42(16) (Show Source):
You can put this solution on YOUR website!
OK, we start by putting together an equation that shows what we know:

Then we can work through and solve it:

So you were correct - the answer is -7. Putting this back into the original equation gives:

It works. So your error must have been somewhere in the calculations when you substituted that value back in. Check over your work again, to see where you went wrong. This is one of the reasons you should always show your working. :-)