Finding The Total Amount
Finding The Total Amount is a Grade 8 math skill in Saxon Math Course 3, Chapter 5, where students calculate the total amount after applying a percent increase or decrease to an original value. This skill combines percent calculation with addition or subtraction and is directly applied to real-world scenarios such as calculating sale prices, tax, tips, and markup.
Key Concepts
Property A percent is a ratio used to describe part of a whole. Use a three row ratio table to find the total by setting up a proportion with the part you know: $\frac{\text{Part Percent}}{100} = \frac{\text{Part Count}}{\text{Total}}$.
Examples 20% of a town voted. If 1600 people did not vote, find the total voters (t): $\frac{80}{100} = \frac{1600}{t}$, so $t=2000$. A recipe uses 30% of a flour bag. If 700 grams remain, find the original amount (w): $\frac{70}{100} = \frac{700}{w}$, so $w=1000$ grams.
Explanation Think of the ratio table as a detective tool! If you know that 60% of your game is complete, you can use that clue to figure out the total time needed to reach 100%. This method connects the part you know to the whole you want to find.
Common Questions
How do you find the total amount after a percent increase?
Multiply the original amount by the percent increase as a decimal, then add the result to the original amount. Alternatively, multiply the original by (1 + percent as decimal).
How do you find the total amount after a percent decrease?
Multiply the original amount by the percent decrease as a decimal, then subtract from the original. Alternatively, multiply the original by (1 minus the percent as decimal).
How is this skill used in real life?
You use it to calculate sale prices after a discount, final price after adding tax, total cost with a tip, and retail price with markup applied.
What is the difference between finding the percent change and finding the total amount?
Finding the percent change gives you the increase or decrease amount only. Finding the total amount adds or subtracts that change from the original to give the final value.
Where is finding the total amount taught in Grade 8?
This skill is covered in Saxon Math Course 3, Chapter 5: Number and Operations and Algebra.