Lesson 4

Lesson Topic: Mental Price Calculation

Goal: For students to be introduced to the idea of quick mental price estimation and addition so they can see how this skill not only may save them from being overcharged at the register, but also will have them paying more attention to what they buy and how much it costs.

Lesson Overview:

1. Class discussion – How much do students know about prices – Play Price is Right game?

2. Video – Middle School Money Matters video 7-4 : Quick price calculation.

3. Review mental addition strategies

4. Student work – class addition game / price addition worksheet

5. Wrap-up or Extension activity

Class Discussion / Questions: Ask the class – Do you think you know generally how much certain things cost? What if you were at the grocery store and you were buying multiple items, do you think you have a general idea how much your bill would be? Let’s play Price is Right!

Price is Right game. Use the grocery item cards provided or feel free to make your own. You could include items other than groceries. Show students the flashcards and have them guess how much each item costs. This could be done one item at a time using a set of student white boards where the teacher holds up the picture of the item, students write what they think the price is and then reveal, teacher writes down the highest and lowest then reveals the correct price, or perhaps the mean and median prices are calculated and then compared to the actual price. Or use the sheet provided and have students fill it in with their estimates as each item is shown then go over them at the end. **Note: Because prices change over time and depending on location, prices for these items are not listed in this resource but should be easily found with a quick Google search.

Finish up: Keep track of the actual prices of the items on the board or have students do it on their sheet. At the end, ask students, without actually adding the items up, to estimate how much the total cost would be to buy this collection of items. Then actually add them up and see how close they were. This is the type of quick addition we are going to practice.

*This is a very useful math skill that if you learn when you are young can help you for the rest of your life. To be able to correctly estimate how much a collection of items will cost together can save you from being overcharged. It’s all about generalizations and practice.

Background Information

There is no real background information for this topic, just examples.

Video – MSMM Video 7-4 Mental price addition - video shows this quick addition practice in action and how it can work.

Activity/In-class work

Mental math addition practice. Students practice adding items in their head using the following strategy (Shown in the video). It is recommended the teacher show the video and also teach the strategy and do some examples with the class.

Example:

Say you have the following 8 items:

Milk $4.79

Bread $2.99

Orange Juice $2.59

Chips $3.29

Chocolate $3.79

Coffee $7.19

Cheese $8.99

Flour $5.29

First you round up or down to the nearest dollar, so milk gets rounded up to $5 and chips gets rounded down to $3, then add them up quickly in your head 5 + 3 + 3 + 3 + 4 + 7 + 9 + 5 = $39 this is your estimated total. The actual total is $38.92 which is very close. They can work with a partner and a timer to practice their mental math addition skill. Use the practice sheet provided or have students create their own lists and then trade.

Mental Math Price estimation and addition worksheet included.

Wrap-up/Extension: Have a class discussion about when this technique might be useful, invent a game around it.