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Tip Estimation

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MCC6.RP.3c - Tip Estimation
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Have you ever ordered lunch and wondered what to tip a waiter or waitress? Well, look at what happened to Sam and Kaitlin.

Sam and Kaitlin went to a small diner for lunch. They had an hour break from work at the supermarket and so it was the perfect time to get a bite to each.

Sam had a grilled cheese sandwich with fries, and Kaitlin had soup and half a turkey sandwich.

Their total bill was $12.90.

Sam and Kaitlin weren't sure how much to tip the waitress. Do you know?

This Concept is all about how to calculate and estimate tips. By the end of it, you will know how to help them with this dilemma.

Guidance

When you eat in a restaurant, you usually pay a tip to the server. A tip is a percent of the cost of the meal. It is also called a gratuity.

When ordering out, you can use estimation to figure out the tip for the server. It is customary to give the server 15% of the total of the meal.

You can use what you have learned about percents to estimate tips.

John ate out for lunch. His total bill came to $12.00. How much should he tip the server?

How can we figure this out?

We know that we need to find approximately 15% of $12.00. 15% is between 10% and 20%. It is easy to find 10% because we can multiply by .10 or move the decimal point one place to the left in the total.

This would mean that 10% of $12.00 is $1.20. If 10% of $12.00 is 1.20, then 20% is 2.40.

We want to choose a number between these two amounts for 15%.

A reasonable estimate would be $1.75 or $2.00.Sometimes people find it easier to calculate 20% using mental math so they often give the server a larger tip because it is easier to figure out!

Now it is your turn. Estimate the following tips.

Example A

A tip on $25.00

Solution: $3.50 - $3.75

Example B

A tip on $18.00

Solution: $2.50 - $3.00

Example C

A tip on $36.50

Solution: $5.50 - $6.00

Now back to Sam and Kaitlin and lunch at the diner. Here is the original problem once again.

Sam and Kaitlin went to a small diner for lunch. They had an hour break from work at the supermarket and so it was the perfect time to get a bite to each.

Sam had a grilled cheese sandwich with fries, and Kaitlin had soup and half a turkey sandwich.

Their total bill was $12.90.

Sam and Kaitlin weren't sure how much to tip the waitress.

To estimate this tip, we can first round up to the nearest whole dollar.

$12.90 rounds up to $13.00.

To tip 15%, we can estimate that 10% is $1.30 and then estimate half of that.

Our answer is $2.00. This is a reasonable tip.

Vocabulary

Here are the vocabulary words in this Concept.

Percent
a part of a whole 100, written using a % sign.
Proportion
two equal ratios.
Sales Tax
a percent added to a total
Discount
an amount taken off of an original price
Tip
15 – 20% of a total bill paid to a server
Gratuity
another word for tip

Guided Practice

Here is one for you to try on your own.

Kelly went to lunch. Her total bill was $29.85. What should she tip the waiter?

Answer

To do this, we can first round the bill up to the nearest whole number.

$29.85 rounds up to $30.00

Next we can use mental math to take 10% of that number and then half of that gets us to 15%.

Our estimate is $4.50.

Video Review

Here is a video for review.

Khan Academy: Rounding to Estimate Sums

http://www.mathplayground.com/howto_percentwp.html - This is a math playground video on how to estimate tips.

Practice

Directions: Estimate the following tips.

1. A tip on $10.00

2. A tip on $18.00

3. A tip on $25.00

4. A tip on $30.00

5. A tip on $15.00

6. A tip on $47.00

7. A tip on $89.00

8. A tip on $121.00

9. A tip on $135.00

10. A tip on $112.50

11. A tip on $127.75

12. A tip on $135.50

13. A tip on $97.78

14. A tip on $88.67

15. A tip on $99.20

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