Question

Gabriela bought a new pair of glasses at the store when they were having a 30%30\% 30% 30, percent off sale. If the regular price of the pair of glasses was $72\$72 $72 dollar sign, 72 , how much did Gabriela pay with the discount?

Answer 1

For this case you can solve the problem by a simple rule of three:
 72 ---> 100%
 x ---> 30%
 Clearing x we have:
 x = (30/100) * (72) = 21.6 $
 Then, we must subtract this value from the original price:
 72-21.6 = 50.4 $
 answer:
 Gabriela pays $ 50.4 with the discount

Answer 2

Since the glasses are 30% off, Garbriela will pay 100% - 30% of the original price, or 70%.  
Therefore, Gabriela will pay $72 * 0.7 = $50.40.   
The value of the discount may be calculated instead. Moving the decimal one place to the left would quickly yield the value of a 10% discount, $7.20. A 30% discount is three times that, or $21.60. Then we subtract this value from the original price of $72.  
$72.00 - $21.60 = $50.40  
The final price Gabriela pays is $50.40.