GEEM - Teaching and Learning

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 of two or three.

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 scenarios on the cards

Note: The students can do all the calculations with a calculator. All the mathematical expressions to find the solutions are given, thus putting the emphasis on the 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.

Bill: $6.25/kg x 0.7 kg = ?

$4.35
$4.37
$4.38
$4.40

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.

Bill: $6.25/kg x 0.7 kg = ?

$4.35
$4.37
$4.38
$4.40

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.

Bill: 1.68 x 52.3 = ?

$87.90
$87.86
$87.87
$87.90

Scenario 3:

A painter is doing a renovation project for a client. She wants to cover the walls with one colour. She estimates that the area of the surfaces to be covered is 3225 square metres and in addition, she will apply two coats on all surfaces. One litre of paint covers approximately 6 square metres of surface.

How many litres of paint does she need to buy?

Number of litres= $\frac{{(2 \times 3225)}}{{6}} = ?$

10 litres
10.75 litres
10.8 litres
11 litres

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 1255 hours.

How many full hours will each student work?

Number of hours: $\frac{{1\;225}}{4} = ?$

313 hours
313.7 hours
313.8 hours
314 hours

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.

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 five index cards by writing one rounding prompt for one decimal number per card.

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

Divide the class into two groups. The first group will hold the cards and the other group will be responding.

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 responding)

Give the starting signal. The responding student will answer the problem on the other student's card. The student holding the card may also read the problem aloud. The responding student must answer and explain their thinking. Once it looks like the students are done, ask the corresponding student to shift one seat to the right. Continue this for the desired period and then repeat with students changing roles.