Today, in class we learned how to calculate percent of a number. This topic, in my opinion, is one of the most important topics a student can learn. Percent of a number is calculated for us all the time: sales tax, discount, a tip at a restaurant, interest rates etc.
Percent of a number questions come in the form of questions like: What is 40% of 80?
I discuss with the students that this is a Language Arts style question. We need to translate this into a mathematical question.
What is 40% of 80? translate into
______ = 40% x 80
The What is a blank, is means =, and of means multiply. We are using calculators in class so they multiply 40% by 80. There is only one problem, our calculator, the TI-83, does not have a percent key. TI assumes that if you are smart enough to use their calculator you are smart enough to know how to type a percent into the calculator. All you do is change the percent into a decimal by moving the decimal 2 places to the left.
_ 32 = .4 x 80
Here are a couple more examples.
What is 25% of 75? - .25 x 75 = 18.75
What is 15% of $120? - .15 x 120 = $18
What is 0.5% of 12? - 0.005 x 12 = 0.06
What is 140% of 8? - 1.4 x 8 = 11.2
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