Finding Original Amounts

 TODAY’S STANDARD: TODAY’S STANDARD:  CCSS.MATH.CONTENT.7.RP.A.3 Use proportional relationships to solve multistep ratio and percent problems. Examples: simple interest, tax, markups and markdowns, gratuities and commissions, fees, percent increase and decrease, percent error. CCSS.MATH.CONTENT.7.RP.A.3  Your goal is to demonstrate your mastery of this topic by solving at least 3 out of 4 (75%) of percent problems correctly on the exit ticket at the end of the period.

 So far we have started with a number, applied a percent change to it, then calculated the final answer.  Example: Start with a $14 item. Apply 9% tax and calculate the final cost.  Example: Start with a $27.45 item. Apply a 30% coupon and calculate the final cost.

 If we know the final amount and the percent change, we can calculate the original amount.  Example: An item at the store is missing a price tag. You take it to the cashier and see the total cost, including tax. If you know what the sales tax percent is, you can calculate the original price on the price tag.

 First, we will write an equation with two variables.  Next, we will replace one of the variables with a number from the problem.  Finally, we will calculate the value of the remaining variable.

 Example: I left a 20% tip. If the tip was $6, how much was the bill?

 Write an equation: tip = 20% of bill t = 0.20 × b

 Example: I left a 20% tip. If the tip was $6, how much was the bill?  Write an equation: tip = 20% of bill t = 0.20 × b  Substitute: tip is $6 so t = 6: 6 = 0.20×b

 Example: I left a 20% tip. If the tip was $6, how much was the bill?  Write an equation: tip = 20% of bill t = 0.20 × b  Substitute: tip is $6 so t = 6: 6 = 0.20×b  Use the inverse operation ÷0.20 ÷0.20 to isolate the variable 30 = b

 Example: The tax on an item was $12. If tax is 8%, what is the original price?

Independent Station  On my webpage under Links for November 13/14, the first activity is eduCanon.  This is a program in which you will watch educational videos and answer questions during the video.

Independent Station  Click Login

Independent Station  Use your Pearson username and password  Pearson username: FirstnameLastinitialIDNumber Example: BobS12345

Independent Station  Click on the Period you are in (there will only be one option)

Independent Station  Click on the circular picture of the math problem to begin the video.  The video has sound, so you must use headphones.

Independent Station  At certain points, the video will pause and a question will pop up.  Choose your answer and press the thumbs up to continue.

Independent Station  After you are done with the eduCanon video, go back to my webpage to access the Google Form.  The Google Form questions will be the same type as the eduCanon video so if you were paying attention you will do well.