A pair of jeans had a 15% off sale. But, when Bill came to buy them a month later the sale was over and he had to pay the regular price of $70. How much money did Bill lose?
15 percent is a more advanced number, so let's break it apart.
10 percent of 70 is 7
5 percent is just half, so 7/2 = 3.5
Thus, 15 percent of 70 is 7+3.5, or 10.5. That means that Bill lost 10.5 dollars by not going to the sale.
A student has passed 60 percent of the 20 quizzes he has written so far successfully. If the student writes 50 quizzes during the year, and passes 80 percent of the remaining quizzes successfully, what is the percent of all successful quizzes for the entire year?
Again, 60 percent is a rather icky number, so lets work with easier numbers.
50 percent of 20 is 10
10 percent of 20 is 2.
That means that the student has already passed 12 classes.
I don't really understand what the second half of the problem is trying to say, so I'll go out on a limb here and say that since he already took 20 quizzes, he has 30 left.
Lets break it up again.
50 percent of 30 is 15.
10 percent of 30 is 3, and 3*3 is 9, which means that 30 percent of 30 is 9
15+9 = 24, and 12+24 = 36
36/50 = .72
The student passes 72 percent of his quizzes for the entire year.
Keep in mind that there are MUCH easier ways to do this, but for me this is the easiest method to explain, thus I use it for multiples of 5. However, this trick won't work with other numbers, such as prime numbers, and you'll actually have to use other tactics.
