You have that the price of a new cellphone is $278, furthermore, the price of the new cellphone has a discount of 30% if an old cellphone is trade in.
In order to determine the amount of the discount you calculate the 30% of the price of the new cellphone.
You divide by 100 the percentage 30, and the result of this is multiplied by the price of new celphone, just as follow:
[tex]\frac{30}{100}\times278=83.4[/tex]Hence, the discount is of $83.40
