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Lesson 2: Percent problems

# Percent of a whole number

Discover how to calculate percentages with a simple example: finding 30% of 6. Learn two methods, using fractions and decimals, to solve this problem. Both approaches lead to the same result, showing that 30% of 6 equals 1.8. Master these techniques for everyday calculations. Created by Sal Khan.

## Want to join the conversation?

• At , how do you turn the improper fraction into a mixed number?
• you can turn an improper fraction to a mixed number by dividing the top number by the bottom number and that is how you do it :)
• I don't understand how Sal turned the fraction into a decimal. How is 4/5 related to 4 divided by 5? (At )
• The slash in between the 4 and the 5 means division. All fractions are division sentences written in a different form. To convert a fraction to a decimal, you divide the numerator by the denominator. For 4/5, you divide 4 by 5 to get 0.8
• Why make these things so complex? I will just divide 6 by 100. And then multiply by 30.
6/100=0.06
0.06*30=1.8

simple as that.
• Sal is showing different approaches that can be used for this problem. Pick one that works for you.

Note: While your method works, you do have a process error. Technically, you treated the problem as 6% * 30 when the problem is 30% * 6 = 30/100 * 6 = 0.3 * 6 = 1.8
• at a scale of 500 percent a measurment is 165mm. what is the actual size?
• The video teaches how to find a percentage of a number, here you're given the percentage and looking for the original number, so you should reverse the operation, and do division.

What is the number when multiplied by 500/100 (that's 500%) gives 165?
? x 500/100 = 165

You can divide 165 by 500/100 to find the answer, or since we're dividing by a fraction, you can just multiply by its reverse, so it becomes likes this:
165 x 100/500 = ?
(165 x 100) / 500 = 16500 / 500
16500 / 500 = 33

The original number should be 33.
• The video teaches how to find a percentage of a number, here you're given the percentage and looking for the original number, so you should reverse the operation, and do division.

What is the number when multiplied by 500/100 (that's 500%) gives 165?
? x 500/100 = 165

You can divide 165 by 500/100 to find the answer, or since we're dividing by a fraction, you can just multiply by its reverse, so it becomes likes this:
165 x 100/500 = ?
165 x 100 = 16500
16500 / 500 = 33

The original number should be 33.
It will help you to understand...if you could then hit a like 👍🏻👍🏻
• this is too quick can someone explain it to me?
• So basically 50% of 100 is 50, and 50% of 5 is 2.5, if you get fractions and decimals then this is easy.
Here is a method to make calculating percentages easier.
Graph paper or any paper recommended
Let's say I want to find 80% of 200, then I would write 200 x 80 (over 100)= ?. The two 0s from the 80 over 100 and 200 cancel out each other. 80 * 2= 160, so 160 is 80% of 200.
Hope this helps
• Can you explain it better Sal other then that Khan Academy is awsome
• Multiply the whole number by 100. The resulting answer is its value as a percentage. Another way is to add a decimal point after the whole number such as 4, and then move the decimal two spaces to the right, fill in each of those empty spaces with a zero, and add a percentage symbol = 400%.
• Sal drawing a dot instead of a multiplication symbol doesn't help my confusion...
• The "." is used instead of "x" since in algebra "x" is a variable and isn't used for multiplication, you will realize later in you math journey it is way better to use a "." rather than an "x"
• I found an easier way to calculate a percent of a whole number.

So 40% of 6 is 2.4
How do we find that?
add a zero to 6 to make it 60 (this is the easier way)
and multiply 6 times 4 to get 24

Now we shift the decimal point to the right and it becomes 2.4.

If you are struggling with that way, you could just find 10% of the number (which is 0.6 in that case) and multiply it by 4.