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### Course: Algebra (all content)>Unit 2

Lesson 12: Old school equations with Sal

# Taking percentages

Taking a percentage of a number. Created by Sal Khan.

## Want to join the conversation?

• How do you do problems like : 36 is what percent of 150?
• You divide 36 by 150, which is 0.24
Then, you take the answer and multiply it by 100%, which is really just multiplying by a 100 then putting a percent sign at the end.
• how do you know if you should multiply or divide?
• If you know what the whole number is and you know what percent of that number you are looking for, you multiply. For example, if you are looking for 20% of 100, you multiply 100 by 0.2. If you want to find what percent of 100 is equal to 20, you would divide 100 by 20.
• Wait, at -, I always thought that .2% also equals .20 as a percentage. Please Help!
(1 vote)
• 100% in decimal form is unity, so .2% is .2/100=.002
• If this helps anyone. I always think that when there is a, "of" then that means divide the two numbers on the left and right of the of. , and "is" means = sign.. So 4=20%x what number. Hope that helps.
• Normally When it says of it means multiply actually all of the time but you can do the reciprocal of the number and then you can divide to get the same answer kind of like 1/2 you can reciprocal it to get to then divide by that number to get your answer
• what is 20 percent of 560
• 560 * .20 = 112
• What is the best way to explain problems like 7(.2) = 70(.02)?
• 7(0.2 = 7(2/10) = 14/10 Reduce by factor of 2: 7/5
70(0.02) = 70(2/100) = 140/100. Reduce by factor of 20: 7/5
They are the same value.

Hope this helps.
(1 vote)
• how do I find the original price if given total price and tax rate
• Great question! Say the tax was 10% and the total was 132. Then the total price was 100% original price + 10% original price, so 110% original price. That's 1.1*original price. Divide 132 by 1.1 (see dividing decimals) and you get 120!
• 60% of what number is 45?. Please show me how to arrive at the answer. Thanks.
(1 vote)
• If you want to do it "the right way", you have to divide 45 by 60 and then multiply the result by 100. If you want to make it easier, knowing that 60/100 is equal to 3/5, you can also divide 45 by 3 and then multiply the result by 5. The result is 75.