Calculating Percentage

In this video, there's a fun little image of an alien and I'm being asked to calculate different percentages from the image.

A percent is a special kind of ratio that expresses parts per 100.

So if I'm being asked what percent of the image does the alien represent? I need to find a way to calculate how many parts per one hundred are covered by the alien.

I'm going to start by counting the number of squares in the alien.

The head is 35 squares plus arms and legs make it 45 squares.

Two halves make a hole, so 46 and 47 total squares.

This entire image is 15 squares by 10 squares which is a total of 150 squares.

I'm going to represent this relationship as a fraction.

The alien covers 47 out of the 150 total parts.

Remember, a percent tells us parts per 100.

So I need to rename this fraction so that it can have a denominator of 100.

There are a lot of different pathways that I can take, but one common way is to get the denominator to one and represent this fraction as a decimal.

47 divided by 150 is .313.

To get it as a percentage, I can multiply both sides by 100.

31.3 out of 100.

Now that it's out of 100, I can just drop the denominator and use the percent sign. 31.3 percent.

If I'm asked to round that to the nearest whole, I will need to round down to 31 percent. That's the portion of this image that the alien covers.

It's possible to be asked a question like what percent of the alien is yellow.

In this case, the whole is now the alien and I'm trying to find the part that's yellow for eight, eight and 1/2 squares are yellow.

I'm going to represent that as 8.5 out of 47.

And now let's get that denominator to 100.

About 18 percent of the alien is yellow.