Question

During a black Friday sale, Alberto paid 158.00 for a cell phone that was reduced by 30%. What was the original price of the smart phone? Please explain how to do this.

Answer 1

The only way to think about this is that the $158 Alberto paid is 70% of the original price.  If you save 30% you pay 70%  (30% + 70% =  100%)

I will put that into math language

$158 = 70% of n   or $158 = .7n  Solve by dividing both sides of the equation by .7
(note that when you divide by a decimal less than 1, the answer will be larger than the starting number - $158 - which is exactly what we want.
To the nearest penny the cost of the phone is $225.71

Many people will try to find 30% of $158 and add it onto $158 but that will not work because the 30% came off the unknown price you are looking for and not the $158. You can't find 30% of a price you don't know. You must talk about it in terms of what you a paying - reread the first thing I wrote at the top of this page.  You can try the wrong way yourself (finding 30% and adding it on)  and when you check it, it won't work.