Math CentralQuandaries & Queries


Question from Kelly, a student:

I know you might be thinking that I didn't look through your previous answers, but I really did.
Here's my dilemma- I have a percent increase equation that is missing the 'old" value.
I know that $65.09 is 70% greater than the average price, but I do not know the average price. How do I go about finding that?
I tried to set up an equation, but its throwing me off because the unknown variable is in there twice, and it's been a long time since I've taken math
Thank you for your help...greatly!


You said

I know that $65.09 is 70% greater than the average price

I let a be the average price in dollars then I see in the statement above as

a plus 70% of a is $65.09


a + 0.70 a = 65.09.

On the left side a is a common factor so

a(1 + 0.70) = 65.09


1.70 a = 65.09.

Dividing both sides by 1.70 gives

a = 65.09/1.70 = $38.28.

I hope this helps,

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