02-NelsonMathGr5-Chap02
6/29/04
3:33 PM
Page 46
CHAPTER 2
9
Reflecting
Rounding Decimals
Goal
1. Suppose Sofia rounded the height to the nearest
whole number. What number would she use to
describe the height?
Interpret rounded decimals, and
round decimals to the nearest
whole and to the nearest tenth.
2. Why might Sofia have rounded to the nearest tenth?
3. How can you round a decimal to the nearest tenth
without using a metre stick or a number line?
Sofia is measuring the height of her room for
a new bookcase. She says it is about 2.8 m high.
rounded the height of the room.
? Sofia
If she gave a more precise measure,
Checking
4. Katrina is having new curtains made for a window in
her room. She needs 1.56 m of fabric. Fabric is sold
in lengths of whole metres and tenths of metres.
How much fabric should she buy? Why?
how might she describe the height?
Karin’s Solution
Practising
5. An electrician needs 6.23 m of wire. Round that length to
the nearest tenth of a metre. Should the electrician buy
that amount or a different amount? Explain.
I want to find numbers that round to 2.8 m.
Sofia rounded the height to the nearest tenth,
so I will look for numbers measured in hundredths.
6. Round each number to the nearest whole number and
to the nearest tenth.
a) 2.78
b) 0.65
c) 8.04
d) 6.90
First I will look for numbers that round up to 2.8.
All of the numbers from 2.75 to 2.80 round
up to 2.8.
7. a) A number rounded to the nearest tenth is 3.9.
What might the number be? List three possibilities.
b) A number rounded to the nearest whole number is 5.
What might the number be? List three possibilities.
8. Fiona says her canoe is about 3 m long.
Meir says his canoe is about 3.2 m long.
Can you be sure whose canoe is longer? Explain.
2.75 2.76 2.77 2.78 2.79 2.80 2.81 2.82 2.83 2.84 2.85
Now I will look for numbers that round down to 2.8.
9. Name two numbers with decimal hundredths that round
to the same whole number but to different tenths.
All of the numbers from 2.80 to 2.85 round down to 2.8.
The height of the room could be any number from
2.75 m to 2.85 m.
46
10. Name a number with decimal hundredths that rounds up to
the nearest whole number but down to the nearest tenth.
NEL
NEL
47
02-NelsonMathGr5-Chap02
6/29/04
3:33 PM
Page 46
CHAPTER 2
9
Reflecting
Rounding Decimals
Goal
1. Suppose Sofia rounded the height to the nearest
whole number. What number would she use to
describe the height?
Interpret rounded decimals, and
round decimals to the nearest
whole and to the nearest tenth.
2. Why might Sofia have rounded to the nearest tenth?
3. How can you round a decimal to the nearest tenth
without using a metre stick or a number line?
Sofia is measuring the height of her room for
a new bookcase. She says it is about 2.8 m high.
rounded the height of the room.
? Sofia
If she gave a more precise measure,
Checking
4. Katrina is having new curtains made for a window in
her room. She needs 1.56 m of fabric. Fabric is sold
in lengths of whole metres and tenths of metres.
How much fabric should she buy? Why?
how might she describe the height?
Karin’s Solution
Practising
5. An electrician needs 6.23 m of wire. Round that length to
the nearest tenth of a metre. Should the electrician buy
that amount or a different amount? Explain.
I want to find numbers that round to 2.8 m.
Sofia rounded the height to the nearest tenth,
so I will look for numbers measured in hundredths.
6. Round each number to the nearest whole number and
to the nearest tenth.
a) 2.78
b) 0.65
c) 8.04
d) 6.90
First I will look for numbers that round up to 2.8.
All of the numbers from 2.75 to 2.80 round
up to 2.8.
7. a) A number rounded to the nearest tenth is 3.9.
What might the number be? List three possibilities.
b) A number rounded to the nearest whole number is 5.
What might the number be? List three possibilities.
8. Fiona says her canoe is about 3 m long.
Meir says his canoe is about 3.2 m long.
Can you be sure whose canoe is longer? Explain.
2.75 2.76 2.77 2.78 2.79 2.80 2.81 2.82 2.83 2.84 2.85
Now I will look for numbers that round down to 2.8.
9. Name two numbers with decimal hundredths that round
to the same whole number but to different tenths.
All of the numbers from 2.80 to 2.85 round down to 2.8.
The height of the room could be any number from
2.75 m to 2.85 m.
46
10. Name a number with decimal hundredths that rounds up to
the nearest whole number but down to the nearest tenth.
NEL
NEL
47