Menu maths: Rounding Decimals
Students will be able to round decimals to the tenths and ones places.
- Discuss with students about a time when their family may have ordered or picked up take out. Talk about how it's important to know how much the bill will be before the delivery person arrives or they go to pick up the food.
- Tell students it's important to know how to round money amounts so they can get a good idea of what to expect. Prices of food or other items for sale are a great way to practise working with decimals in the real world. It is helpful to know how to estimate total prices by rounding.
- Introduce the concept of Estimating, or roughly calculating, the total cost. Discuss with students how when they use this skill in the real world at a store or while making some other purchase, they will likely estimate the total cost rather than find the actual cost.
- Tell students that today they will order pretend takeout foods for their friends or family. Show students the takeout menus you've collected to get them excited about the lesson.
Explicit Instruction/Teacher modeling(15 minutes)
- Show students a large menu on chart paper or projected at the front of the class.
- Tell students that you will pick out several dishes for yourself and your family.
- Discuss with students that in this instance we can round to get an approximate total so we know how much money to have available to pay. Ask students whether it is more beneficial to round to the tenths place or ones place.
- Model choosing several meals and rounding each amount first to the tenths place and then to the ones place.
- Compare the two totals and discuss which is more accurate.
Guided practise(20 minutes)
- Divide students into groups of three. Tell them to pretend that they will be ordering from a restaurant together. All students will select a food and drink.
- Have students list the items by the price listed on the menu on lined notebook paper. Next to each price have the students practise rounding to the tenths place. All students in the group should record their group members' orders.
- After students have completed this step, have them add each meal together to get a grand total.
Independent working time(15 minutes)
- Have students switch menus at this time if they would like to do so. Tell students to select a meal and drink for each member of their family. Have the students round each price to the ones place this time. Make sure students record their choices on notebook paper.
- For students in need of support, have them focus solely on one meal and drink for themselves. Have the student round to the tenths place and compare to the actual price.
- For students in need of a challenge, have them select one meal and compare the price on menus from multiple restaurants. Ask the student to think about if it's easier to notice differences in prices when rounding to tenths or ones places.
- Read aloud the following problem for students to solve: "I went to dinner with my mom and brother. My mom ordered chicken soup which cost $8.90. My brother ordered mac and cheese which cost $5.49. I ordered a veggie wrap which cost $6.40. Estimate the total price for the three dishes by rounding to the nearest tenths place."
- Have students complete the assessment in their maths journals independently before checking their answer with a partner. Make sure students show their work.
Review and closing(5 minutes)
- Gather students together and discuss the benefits to rounding. Ask students to describe any common errors they or a group member may have made and that they should look out for.
- Invite several students to share their orders and explain their thinking as they rounded to find a total.