a. So the electric guitar is sold for a sale price of $315 after the discount. The discount was 30%. Even though we get that amount off, we still pay 70% of the original price, because 100% (original price) - 30% is 70%.
b. An equation that can help us find the regular price of the item is through writing and solving a proportion. Set it up like this:
315/x = 70/100
This is because 315 is part of the whole and is 70% of the value of x.
How to solve it:
Okay. Let's solve this by cross multiplying the values. 315 * 100 is 31,500. 70 * x is 70x. That simplifies to 31,500 = 70x. Didivde each side by 70 to isolate the x. 70x/70 cancels out. 31,500/70 is 450. Let's check this by multiply the number by 70% and see what happens. 450 * 70% (0.7) is 315. There. x = 450. The regular price was $450