As we discussed in pre-algebra, percent is a ratio that compares
a number to 100. Percent means per hundred. Percent is usually
expressed with the percent symbol %.
Percent problems are usually solved by using proportions.
Example:
In a classroom 14 of the 21 students are female. How many
percent does that correspond to?
We know that the ratio of girls to all students is
And we know that this ratio is a proportion to a ratio with the
denominator 100.
As we saw in the last section from here we can calculate x
i.e. 67% of the students in the class are female.
One of the ratios in these proportions is always a comparison of
two numbers (above 14/21). This numbers are called the percentage
(14) and the base (21). The other ratio is called the rate and
always has the denominator 100.
Another way of saying this is that
Percent of change, or p%, indicates how much a quantity has
increased or decreased in comparison with the original amount. It's
calculated as:
Example:
Johnny is at the store where there is a big sign telling him
that there is a $4.99 discount on a shirt that originally costs
$39.99. But how big is the discount in percent?
The prize of the shirt has decreased by 12%.
Videolesson: A prize increases from $500 to
$585. How big is the increase in percent?