Interpreting Decimals
A decimal point is used whenever a number or part of a number is below 1. This partial number will always be to the right of the decimal point.
For example, if we have the number 0.5 of a dog treat,then we don’t have a whole treat, just a half of one. Same applies to 2.9 dog treats. With 2.9, we have two whole treats and a third one that is not quite whole. Liesel must have taken a bite out of that third one.
Know Your Place Value
We touched briefly on decimals on the place value page. If you haven’t looked over place values yet, please make sure you are confident with them before starting decimals and percents. The reason is place value is super important to decimals. You may be asked to round a decimal to the nearest tenth, hundredth, or so on. If you don’t know your place value, then you can’t round correctly.
Remember! If the rounding number is below 5, then round down. If the rounding number is 5 or above, then round up!
Percents
To change a decimal to a percent, multiply the decimal by 100. Seriously, that is all you need to do. You can revert back to a decimal by dividing the percent by 100.
Percent Math Problems
You will probably get a question or two asking how much interest was earned, finding the discount or finding the markup on an item.
Interest Earned
To calculate interest earned, you need to multiply three key bits of information: principal, rate, and time. Principal is the initial amount of money, rate is refers to the interest rate (that is the percent in the problem), and time is how long the interest will be earned.
Liesel invested $500 in a savings account at First Savers Bank at a rate of 3%. She plans to keep it in the account for two years. At the end of the two year period, how much money will Liesel have?
Interest earned over a span of two years is $30. After calculating interest, we added it to the original principal to get the total amount that Liesel would have in the account after two years.
Finding the Discount or Markup
Knowing how to answer this type of question will be useful in your daily life. If you are in a store and an item is marked a certain percentage off, can you determine what the new price will be? In order to answer this question, convert the percentage to a decimal, then multiply that by the original cost. If you are finding the discount, subtract the answer from the original amount. To find the markup, add the answer to the original amount.
Textbook Central marked up the cost of a book by 40%. The company’s cost to purchase it wholesale was $10. Liesel is the customer wanting to purchase the book from Textbook Central. She has a 20% coupon to use. How much is the retail cost (markup) of the book? How much does Liesel pay for the book after the coupon (discount) is applied?
Be careful with the wording of these problems. Sometimes the problem is just asking what the markup or discount would be rather than a total price; however, the answer choices might list them all as a possible answer.