what was the original price of a radio that sold for $70 during a 20% -off sale ?

Question

Question :          

A certain radio coasts a merchant $ 72 . At what price must the merchants sells this radio in order to make a profit of 20% of the selling price ? 

Answer 1

Let x = original price; sale price = $70 = 0.80x since 20% off means "80% ON!

 

Now just solve for x in the eqation I wrote, above, where 0.80 represents 80% of original price.