To solve problems with percent we use the percent proportion
shown in "Proportions and percent".
x/100 is called the rate.
Where the base is the original value and the percentage is the
new value.
Example:
47% of the students in a class of 34 students has glasses or
contacts. How many students in the class have either glasses or
contacts?
16 of the students wear either glasses or contacts.
We often get reports about how much something has increased or
decreased as a percent of change. The percent of change tells us
how much something has changed in comparison to the original
number. There are two different methods that we can use to find the
percent of change.
Example:
The Mathplanet school has increased its student body from 150
students to 240 from last year. How big is the increase in
percent?
Method 1:
We begin by subtracting the smaller number (the old value) from
the greater number (the new value) to find the amount of
change.
Then we find out how many percent this change corresponds to
when compared to the original number of students
Method 2:
We begin by finding the ratio between the old value (the
original value) and the new value
As you might remember 100% = 1. Since we have a percent of
change that is bigger than 1 we know that we have an increase. To
find out how big of an increase we've got we subtract 1 from
1.6.
As you can see both methods gave us the same answer which is
that the student body has increased by 60%
Video lesson: A skirt cost $35 regulary in a
shop. At a sale the price of the skirtreduces with 30%. How much
will the skirt cost after the discount?
Video lesson: Solve "54 is 25% of what
number?"