B1.6 Round decimal numbers to the nearest tenth, hundredth, or whole number, as applicable, in various contexts.
Activity 1: Rounding in Context - The Debate! (Rounding a Number to the Nearest One, Tenth or Hundredth)
Present or write different scenarios on cards.
Group the students into teams (2 or 3 people).
Use the same cards for each team.
The student must choose the correct rounding based on the context. The student's justification is paramount.
Examples of questions to ask students
- Why did you choose this answer? What arguments do you use to justify your choice?
Examples of scenarios on the cards
*The student does all the calculations with a calculator. All the mathematical expressions to find the solutions are given, thus emphasizing the concept of rounding.
Which of the choices is the correct rounding?
Scenario 1(a):
- At the market, tomatoes sell for $6.25/kg. My aunt buys 0.7 kg. She pays with her credit card.
- 4,35 $
- 4,37 $
- 4,38 $
- 4,40 $
Bill: $6.25/kg x 0.7 kg = ?
Scenario 1(b):
- At the market, tomatoes sell for $6.25/kg. My aunt buys 0.7 kg. At the cash register, she pays in cash.
- 4,35 $
- 4,37 $
- 4,38 $
- 4,40 $
Bill: $6.25/kg x 0.7 kg = ?
Scenario 2:
- The price of gasoline fluctuates daily. Today, gasoline sells for $1.68/litre. It takes 52.3 liters to fill up. The driver pays with a credit card.
- 87,90 $
- 87,86 $
- 87,87 $
- 87,90 $
Bill: 1.68 x 52.3 = ?
Scenario 3:
- A painter is doing a renovation project for a client. He wants to cover the walls with one colour. He estimates that the area of the surfaces to be covered is 3 225 square feet and in addition, he will apply 2 coats on all surfaces. One gallon of paint covers approximately 400 square feet of surface.
- 16 gallons
- 16.12 gallons
- 16.13 gallons
- 17 gallons
How many gallons of paint does he need to buy?
Number of gallons= \(\frac{{(2 \times 3\;225)}}{{400}} = ?\)
Scenario 4:
;- A company hires 4 students for the summer. The terms of the project require each worker to work the same number of hours. In total, there is funding for 1 255 hours.
- 313 hours
- 313.7 hours
- 313.8 hours
- 314 hours
How many full hours will each student work?
Number of hours : \(\frac{{1\;225}}{4} = ?\)
Scenario 5:
- The Grade 8 students are organizing an end-of-year trip to Ottawa. In order to get to their destination, the organizing committee is renting buses. Each bus can accommodate a maximum of 62 people. With the chaperones, there are 213 people who will be on this trip.
- 3
- 3,4
- 3,5
- 4
How many buses does the committee need to rent to accommodate everyone and minimize costs?
Number of buses : \(\frac{{213}}{{62}} = ?\)
Activity 2: Express Friendship (Rounding Decimal Numbers)
Materials
- Cardboard sheets, cardstock or cue cards 10 cm x 6 cm
- felt-tip pen
Each student prepares 5 index cards with one decimal number written per card.
Divide the class into two groups. Thefirst group will be the one with the cards and the other group will be the one answering the questions.
Arrange chairs, side by side, corresponding to half the total number of students.
Opposite each chair, place a second row of chairs (1 metre apart).
X X X X X X X X (students with cards)
O O O O O O O (students questioned)
Give the starting signal. The student has 20 seconds to answer the problem listed by the other student. The student may also read the problem on the card. The student must justify their answer (rounding) to the student in front. Thereafter, every 20 seconds, the students answering the questions must move one seat. Continue this for the desired period. After this period, students change roles.
Examples of cards
Sheet 1 : Round the number to the nearest tenth. Justify.
2,071
Sheet 2 : Round the number to the nearest whole number. Justify.
0,09
Sheet 3 : Round the number to the nearest hundredth. Justify.
9,074