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Percent Change

- Show lesson plan & teacher guide
- Show answers to discussion questions
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- We’ll learn how to to solve multi-step percent problems.
- We’ll also learn how to calculate percent increase and percent decrease.
- And we'll see how this knowledge can help us buy items on sale, learn about different schools, and see how much our things are worth!
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Discussion Questions
- Before VideoWhat is a percent? Can you give an example?ANSWER
A percent is a ratio out of 100. 34% is 34 out of 100.
To write a percent as a fraction, write the number as the numerator over denominator 100, and then simplify. For example, 34% is [ggfrac]34/100[/ggfrac] or [ggfrac]17/50[/ggfrac]. To write a percent as a decimal, divide the number by 100. 34% = 0.34.
I change the percent to a decimal then multiply by the whole. 34% of 50 is 0.34 × 50 = 14.
percent = [ggfrac]part/whole[/ggfrac]. First, write a ratio of [ggfrac]part/whole[/ggfrac], and then divide to write it as a decimal. Multiply by 100 to write the value as a percent.
percent = [ggfrac]part/whole[/ggfrac], so whole = [ggfrac]part/percent[/ggfrac]. Write the percent as decimal, and then divide the part by the decimal to get the value of the whole.
- After VideoHow can you tell if the problem you want to solve is a percent increase or percent decrease problem?ANSWER
I can look for keywords such as "more" or context-based words like “tax” or ”tip” to identify when the value is increasing. I can look for keywords such as "less" or context-based words like "discount" or "sale" to identify when the value is decreasing.
First, I calculate the part that represents the percent increase by multiplying the percent by the initial amount. Then, I add that amount to the original amount.
First, I calculate the part that represents the percent decrease by multiplying the percent by the initial amount. Then, I subtract that amount from the original amount.
First I subtract to find the difference between the original and increased amounts. Then I divide by the original amount to find the percent change as a decimal. Multiply by 100 to write it as a percent.
It is the same process as for an increased amount. First I subtract to find the difference between the original and decreased amounts. Then I divide by the original amount to find the percent change as a decimal. Multiply by 100 to write it as a percent.
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Vocabulary
- Ratio DEFINE
Shows the relationship between two quantities.
- Percent DEFINE
A ratio out of 100.
- Two-step problem DEFINE
A problem that requires two separate steps to solve.
- Percent increase DEFINE
When the value of a quantity increases by a certain percent, leading to a value that is more than 100% of the original value.
- Percent decrease DEFINE
When the value of a quantity is decreased by a certain percent, leading to a value that is less than 100% of the original value.
- Pie chart DEFINE
A special chart (data display) that divides a circle into sectors. Each sector shows a percent of the whole.
- Ratio DEFINE
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Reading Material
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Practice Word Problems
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Practice Number Problems
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Lesson Plan
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Teacher Guide