Unit 8: Percent
Percent as a ratio out of 100, and the everyday math of change, interest, tax, and tip built on top of it.
5 topics · 18 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
What Percent Means
- How it worksHow does converting a percent to a decimal or a fraction out of 100 let you use it in any calculation?
- Worked exampleFind 25 percent of 60 and write 25 percent as both a fraction and a decimal.
- Common mistakeWhy can a percent be bigger than 100, even though it sounds like it should be a piece of a whole?
Your turn1 of 2
A survey found that 66 percent of students walk to school. Write that percent as a decimal.Percent of a Number
- How it worksHow do you turn 'find 8 percent of 50' into a multiplication problem?
- Worked exampleFind 8 percent of 50 dollars.
- Worked exampleFind what percent 15 is of 60.
- Common mistakeWhy doesn't finding 8 percent of a number mean dividing that number by 8?
Your turn1 of 2
Priya wants to save 42 percent of her 198 dollar paycheck. How many dollars is that?Percent Increase and Decrease
- How it worksHow do you find the percent change between an original amount and a new amount?
- Worked exampleFind the percent increase when a 40 dollar jacket goes on sale for 30 dollars, then goes back up to 40 dollars.
- Going furtherWhat happens to the percent change formula when the new amount is smaller than the original amount?
- Common mistakeWhy doesn't a 20 percent decrease followed by a 20 percent increase bring a price back to where it started?
Your turn1 of 2
A jacket that normally costs 79 dollars goes on sale for 21 dollars. What is the percent decrease?Simple Interest
- How it worksHow does the simple interest formula turn a principal, a rate, and a time into the interest earned?
- Worked exampleFind the simple interest earned on 500 dollars at 4 percent per year for 3 years.
- Common mistakeWhy doesn't simple interest earn interest on the interest you've already earned?
- Going furtherWhat happens to the interest earned when the number of years doubles but the rate and principal stay the same?
Your turn1 of 2
Nina deposits 1423 dollars in a savings account earning 7 percent simple interest per year. How much interest does she earn after 9 years?Tax and Tip
- How it worksHow do you add a percent-based tax or tip on top of a bill's original amount?
- Worked exampleFind the total cost of a 45 dollar meal with 8 percent sales tax and a 20 percent tip.
- Ties togetherHow does calculating tax and tip use the exact same percent-of-a-number skill as finding a percent increase?
Your turn1 of 2
Sam's restaurant meal costs 73 dollars before a 8 percent sales tax. What is the total cost?