Astadium's normal ticket price is $78. as a special promotion they offer 15% off. what is the price of the discounted ticket?

You have to find out what 15% of $78 dollars is.  If you have to do this in your head and not on a calculator you can find 10%, then cut that number in 1/2 and add it to the answer.  So 10% of $78 is 7.8 so $7.80.  You can divide 7.80 by 2 and get 3.9 and add that to 7.8 which is 11.70.  So 15% of $78 is $11.70. 

The answer is 66.5 the offer is 15% off so you multiply 78 by .85 (15% off) which gives you the answer 66.5