Ratios &
Percentages:
Fraction Into Decimal
Into Percent,
And a Work of Art
Today's
Snack: A
person who is ages 11-14 needs about 50 milligrams of vitamin C per day. A
medium-sized orange has 50 milligrams of vitamin C. How much of your
recommended daily intake of vitamin C will one orange provide, if you are that
age? So why don't you eat one right now? And enjoy a glass of 100% cold water.
--------------------
Supplies:
Adult writes problems on a board or
poster paper
Students use scratch paper and
pencil to solve
Extra scratch paper | colored
pencils | rulers | scissors | gluestick
Colored construction paper or
colored laser print paper
There are lots of good reasons you
should know how to convert a fraction to a percent.
Why are you rolling your eyes? Yes,
there are!
Truly, outside of math class, there
are many, many times when it will come in handy for you and help you think
mathematically and correctly. In cooking . . . in building projects . . . in
fixing machines . . . in buying real estate . . . there are tons of times it
will help you to know that ½ equals 50%, etc. etc. etc.
So . . . let's do this!
Think of a fraction as being a
percent that just needs to be put in relationship to 100. A percent is simply a
ratio of some number to 100. Percents are always in hundreds.
A lot of numbers are evenly
divisible into 100, such as 2, 4, 5, 10 and so on, so those are easy to change
from a fraction into a percent. For example, we know that 2 x 50 = 100. So we
would write:
½ = 1 x 50 / 2 x 50 = 50/100 = 50%
Use this process to find the
percents that are equivalent to these fractions, that easily fit with a
denominator of 100:
¾
+ ___%
2/5
= ___%
3/10
= ___%
4/25
= ___%
But for most other numbers, that
can't be divided evenly into 100, you have to use the following method:
1.
Write the fraction as a decimal. Figure it out by dividing the numerator
by the denominator. So for the fraction 5/8, to write it as a decimal:
5 ÷ 8 = 0.625
2.
Write the decimal as a percent. You simply move the decimal point over
two places, which means you multiply it by 100 to see how many hundredths it
is. In this case, the percent is 62.5 hundredths, or 62.5%.
3.
Check to make sure it makes sense. You know that 5/8 is slightly more
than half, which would be 4/8. So the decimal is probably right, 0.625, which
is slightly more than 0.5, or one-half. Therefore, the percent of 62.5% is
probably right.
Now let's make a work of art that represents this
math skill!
Fold a piece of colorful construction paper or
laser-print paper in thirds. You should have three equal sections. It doesn't
matter if they are vertical or horizontal. Smooth the paper out so that it lays
flat.
Now figure out on a piece of scratch paper what
decimal and percent this fraction represents:
4/5
Using extra scratch paper and the
art materials, write the word "fraction," using the colored pencils to make it
really stand out. Then cut it out, and glue-stick it to the one-third of the
page that's on the left.
Next, write the fraction as a decimal,
and also decorate it, cut it out, and glue-stick it in place in the center
section of the paper.
Last, write the fraction as a
percent, and decorate, cut and glue-stick as you did with the others . . .
except also take a piece of scratch paper and cut it into 100 equal pieces. You
may need a ruler to get that done.
Then, using colored pencil, color
the same number of the 100 equal pieces as the percent that you calculated. You
should end up with some little pieces of paper colored, and some left plain.
Using a gluestick, glue the colored
pieces of paper in one clump, and then glue the white pieces of paper next to
that clump.
That should show very plainly what
percent equals 4/5.
Besides, you will have a pretty
picture to display and help you remember!
