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# Hey, I really need help understanding this linear equation. Can someone please explain this to me?

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Catherine paid \$155.87 for an MP3 player. If the price paid includes a 9% sales tax, which of the following equations can be used to determine the price of the player before tax? How much was the MP3 player before tax?

a) y = 1.09x

\$143.00

b) y = 1.09x

\$166.90

c) y = 1.9x

\$166.90

d) y = 1.9x

\$143.00

Oct 4, 2020

#1
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Let  x  be the original price and let  y  be the price after tax.

Then...

the price after tax   =   the original price + 9% of the original price

y    =    x   +   9%  of  x

y    =    x   +   0.09  *  x

y    =    x   +   0.09x

y    =    1.09x

Then, to find the original price when the price after tax is  155.87,  plug in  155.87  for  y

155.87   =   1.09x

155.87 / 1.09   =   x

143   =   x

So the original price is  \$143.00

Oct 4, 2020
#2
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THANK YOU SO MUCH!! I'm going to write this out and see if I can remember how to do it. Do you think you could help the guy who posted before me as well?

SmartMathMan  Oct 4, 2020
edited by SmartMathMan  Oct 4, 2020