Mental Percents
Lesson 3

1. Start the lesson with a question to the students using a tipping situation in a restaurant.
1. What is the appropriate tipping % in a restaurant? (15%, 17%, 20%)
2. If your bill is $52.78, how would you go about tipping 15%? (Make sure all calculators, pens, pencils, etc. are not being used for maximum effect)

1. Allow students some time to think out the solution. Question several students on their thought processes.
2. Educate students on the 10% rule using the following examples:
1. $3.00
2. $18.00
3. $54.65
4. $123.45…etc.

 

1. Now go back to the original problem.
1. First round to the nearest whole dollar.
2. Then find 10%.
1. Round again if necessary

1. Then find half of 10% (which is 5%)
1. Round again if necessary
2. Add the two together and you have your approximate tip.

 

1. Go through process again using the amount $44.80
1. Give the students one minute to try.
2. Go through steps above until you arrive at your answer.

1. Do as many examples as necessary until you feel the class has confidence in doing them on their own.

 

2. Store sales
1. What are some of the common sales you see in retail or department stores?
2. Are the markdowns on the merchandise or at the register?
3. How do you know if you are getting the correct discount?

1. Share a few personal stories here.

4. Situation 1: The store has a 30% off sale and the item you are buying is marked at $35.99. What should your discount be?

1. See if students apply the 10% rule to the problem.
1. Round the amount to $36.00
2. Take 10% by moving the decimal one place left.
3. Round if you need to the nearest dollar.
4. Then multiply by 3 and you have your discount.
1. Explain that 3 x 10% = 30%.
2. Do another 30% problem if necessary.

5. Situation 2: The store has a 60% off sale and the item you are buying is marked at $74.25. Find the approximate discount.

1. Go through the same steps above except this time show students that 6 x 10% is 60%.
2. Do another if necessary.

6. Situation 3: The store has a 50% off sale, but today you save an additional 25%.

1. Ask the students if this means they will save 75% total?
2. Go through the following steps and see.
1. First find 50% off (Either half off or 5 x 10%)
2. Then take 25% off that amount (either one fourth of the amount or go through steps like a tip: Find 20% and then add half of 10% to it)
3. Then take the original amount and find 75% off. (Some students can do fourths, some will find 70% and 80% and determine the number in the middle, and lastly some will find 70% and add 5% to it. Anything mathematically correct is acceptable when doing mental percents)
4. The discount found from step 2 will be less than that found in step 3. Discuss why.

7. If a store has a sale 75% off, plus additional 20% off, plus and additional 5% off if you use your store credit card, will that mean you get it for free?

1. Can your store purchase ever come out to free?
2. Have students research the Sunday paper over the next few weeks for sales that have these types of advertisements in them.

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