Problem Solving Strategies-percent off sale price

10%off means 90% of the original price
25%off means 75% of the original price
80%off means 20% of the original price 


For this kind of problems:
Always go directly to calculate the percentage of the original price after discount
 That is the Remaining Value 


Step1: find what percentage  of the original price after discount(%)
Step 2: find the discount price (the remaining value)
            the original price x (1- discount percentage) 


EX: A ball sells for $10, There 's 30% off on Friday.  How much you need to pay after discount?


10x(1-0.3)=7


Application Word Problems :


1, school-coundown-47-2008(99)

If Jimmy increases a number by 10% and then decreases this new value by 10%, what 

percent of the original number will the final result be?

2, At Pacific Middle School, 40% of the students are boys. 20% of the boys play a musical instrument. Half of these boys play brass instruments. If there are 14 boys who play brass instruments, what is the total number of students at Pacific Middle School?

3, An oil tanker containing 108,000 gallons of oil releases one third of its remaining volume every two hours. How many gallons have been released after the first six hours?(76000)

4,A computer virus destroys computer memory. On the first day it destroyed ½ of this memory. On the second day it destroyed 1/3 of the memory remaining after the first day; on the third day it destroyed ¼ of the memory remaining after two days and on the fourth day it destroyed 1/5 of the memory remaining after three days. What part of all the computer memory was left after those four days? (1/5)

Solution : 

Problem Solving Strageties: Fractions

More Study :

Mathcounts Notes