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You bought a phone for $640.00. It has been on sale for 20% off. What was the phone's original price?

 Sep 11, 2017
 #1
avatar+106536 
+2

Let the original price   = P

And 20% off  the original price   = .20P

 

So

 

Original Price -  [ 20% off ]  =  640     ...  so..

 

P  - .20P  = 640       simplify

 

.80P  =  640        divide both sides by  .80

 

P = 640 / .80  = 800

 

So.....the original price was $800

 

 

cool cool cool

 Sep 12, 2017
 #2
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The original price is $800.00

 Sep 12, 2017
 #3
avatar+1904 
0

Let x = phone's original price

Let 0.2 (20%) = discount of phone

Let 640 = price of phone after discount

 

\(0.2x=x-640\)

 

\(0.2x-x=x-640-x\)

 

\(-0.8x=x-640-x\)

 

\(-0.8x=-640-0\)

 

\(-0.8x=-640\)

 

\(\frac{-0.8x}{-0.8}=\frac{-640}{-0.8}\)

 

\(1x=\frac{-640}{-0.8}\)

 

\(x=\frac{-640}{-0.8}\)

 

\(x=800\)

.
 Sep 12, 2017

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