Video and Examples
If you know are given the percent and the part, how much is the whole? Sample:
This is 30% of the apples in the barrel. How many apples are in the entire barrel?
This is 30% of the apples in the barrel. How many apples are in the entire barrel?
To solve this question, we need to remember that 100% represents the "whole" or "the entire thing". In this problem, we do not know how many apples represent 100%, but we do know that 6 apples are equal to 30%. 
There are many ways to solve the above problem. Here are a few of them:
Method 1  Method 2  Method 3 
Since 6 apples equals 30%, each apple is 5%. 5 x 20 = 100, so there are 20 apples. 
NOTE: This proportion was set up by putting 6 and 30% on top, since 6 apples equals 30%. 
All three methods will lead to the same answer  there are 20 apples in the entire barrel.
Example 2
Jennifer scored 12 points for her basketball team. If this was 40% of the total points scored, how many points did her team score altogether?
SelfCheck
Question 1 This is 60% of the band. How many musicians are in the whole band?

[show answer] 
Question 2 These are 8% of the cars in the parking lot. How many cars are in the parking lot?

[show answer] 
Question 3 This is 40% of the birds in the cage. How many birds are in the cage?

[show answer] 