Math Contest!

Last Monday, we took part in a Canadian Math Competition. At the beginning, it was quite nervous and people were chatting anxiously. When we received our answer sheets and booklets, I felt more relaxed as I started to do the math. The first few questions were quite simple, but as I worked on, they got harder and harder. I managed to complete most of the questions with some confidence. I thought I did really good at the beginning, but not so good at the end. I tried not to guess any questions, but some of them I wasn't sure about. I felt that I did really good and it was easier than I thought, but when we went over a question I was confident about, I discovered that I got it wrong. I will show you one question that was on the contest that I liked and how I solved it:
12. The price for each item at the Gauss Gadget Store has been reduced by 20% from its original price. An MP3 player has a sale price of $112. What would the same MP3 player sell for if it was on sale for 30% off its original price?

A.) $78.40 B.) $100.80 C.) $89.60 D.) $168.00 E.) $98.00

First, to solve this problem, you have to figure out how much the MP3 player cost at full price. Because I forgot how I solved this problem two months ago, I will use the tried and true guess-and-check method. You just multiply a number by 0.8 until you get 112. First, I plugged in 150 and got 120. Then, I tried 145 and got 116. Eventually, I got 140. From here, solving this problem is easy. You just multiply 140 by 0.7 and you will get your answer, which is E.) $98.00.
I did pretty good this time around and hope to do better next year!