The first thing to remember: «ninety percent of forty» it's written as «90% of 40». The symbol «%» is often used to make the mathematical expression shorter.
When they talk about 90% of something, they mean that we need to take 90 fragments of the something Whole. One percent means part per one hundred all the time. And we must remember the rule: «The sum of all parts of the whole is 100%». In fact, you have to divide 40 into 100 fragments and take 90 of them. Let's try to figure it out together. You can find out how much 90% of 40 in several ways.
This site below shows some of these methods and an illustration that will help visualize 90% of 40. By the way, people who learn how to calculate 90% of 40 will be able to do the same with other numbers later. Explore that we have presented for you and get a complete understanding of the topic of interest.
As a bonus to the lesson at the end you will know what is not equal to 90% and learn how to solve this problem too.
Memorizing the formula for calculating percents is the easiest way to solve the problem "What is 90% of 40?”. That's why this method is taught in mathematics lessons of schools, because you do not need to know anything about fractional numbers or proportions. Learning the formula will be enough for calculating. The main thing is to correctly determine its components.
The general formula for calculating percentages looks like that:
There are 40 is the Whole, and 90 is the Percent, but the X is the desired result.
So, you can to get an answer to the question «What is ninety percent of forty»:
Now you know that 90% of 40 it is equal to thirty six!
If you know how to deal with decimal numbers, then you can use another method. You may to convert the percent as a decimal number. It is easy. You can do this by dividing 90 by 100. Just move the decimal point 2 places to the left. So, 90% in decimal form is equal to 0.9
And next just multiply the resulting decimal number with a Whole (with 40):
You get 36 again! So, we can use equivalent forms of percentages interchangeably and choose the one(s) that best suit our purpose.
It is a good method which can show you what is 90 percent of 40. Recall that 40 is a Whole, and a Whole is 100 Parts.
Let's make an equation from this proportion to calculate the Part. We need to multiply the numbers cross by cross:
Let's solve this equation and find the unknown:
So, 90% of 40 it is 36 again.
Look at the diagram we have drawn for you. It shows 90% of the Whole. The pie chart has 40 fragments, and the blue fragment of the circle is 36, or 90% of 40.
Interestingly, the diagram of 90% from any integer will look the same. Because it is always 90 parts of 100 something. Although the answer to the problem will be different, the picture will be the same. For example, 90% of 100 would be 90, which is 90 parts of 100 parts. And the blue part will always take up 90 percent of the circle, because it's always 90 parts of 100.
Since you know the sum is 100%, so to calculate «What is not equal to 90%» you can subtract 90% from 100%. The next step is to take that percents from 40 (we used the formula again):
Or just subtract 36 from 40:
The lesson is over. We hope that we have shown everything clearly enough for you to become a real expert.