Percent

Percents The goal here is to understand that percent means out of one hundred. You and I, just a few short years ago, were probably taught a different way to do these kind of problems. For example:

16 out of 25 is what percent?

__16__ = __x__ 25 100

% = part ÷ whole and then plug in the numbers.

[|Proportion Method]

When kids memorize formulas, they often don’t understand what they are doing and, as a result, do not remember what they have learned. They need to be shown how to do one and then they can do the rest. My goal for students is to have them understand what they are doing and why they are doing it. Too often a student who is taught only one of the methods above cannot do a simple problem like: 20 out if 50 is what percent? I am hoping that when a student sees a problem like this, they turn it into “out of 100” by doubling both numbers because that is a fair thing to do. If a student can see that 20 out of 50 is the same thing as 40 out of 100 it shows a greater understanding of percents. This is also easily tied into fractions.

When they try the first problem mentioned above, it is my hope that they see that 25 can easily be made into 100.

16 x 4 = 64 which is the same as 64% 25 x 4 =100

Or, another way to look at the problem is when someone makes 16 out of 25, if they continue making 16 out of 25 until they take 100 shots, we will have a percent because percent means "out of 100".

16 / 25 16 / 25 16 / 25 16 / 25 64 / 100 which is 64%

This helps with the understanding that percent is something out of 100. Too often I see kids put down 34 out of 40 on a paper and then write 34% at the top.

Again, the goal in math is to understand it, not just do it.

What is 20% of 300?

Traditional ways teach us to change 20% to a decimal and then multiply it by 300. We will use that method to find percents later this year. These types of problems, however, can be done mentally. We have looked at ways to do 10% and found that 10% of a number (dividing by 10) allows us to move the decimal over one spot and in cases of numbers that end in zero, a zero can be dropped.

10% of 40 = 4 10% of 90 = 9 10% of 1400 = 140 10% of 28 = 2.8

Understanding this allows one to figure out many other percents without using paper and pencil.

20% is the same thing as 10% + 10% or 2 x 10%.

20% of 40 = 4 + 4 = 8

30% of 40 = 3 x 4 = 12

These are not “calculator” problems, nor are they “paper and pencil” problems. With some basic understanding of percent, students should be able to figure these out in their head.

Mr. Peterson