4b workbook answers (prac 7

Chapter 10: Decimals (2)58

Name: Class: Date:

Chapter 10: Decimals (2) 59

Practice 7 Estimation Of Decimals

(1) Round off each number to the nearest whole number.Then estimate the sum or difference.

(a) 7.7 ! 12.3 (b) $2.90 ! $7.15

(c) $9.05 ! $19.55 (d) 21.8 " 11.5

(e) 35.67 " 15.09 (f) $15.40 " $5.95

(7) Divide. Round off your answer to the nearest tenth (1 decimal place).

(a) 7 # 8 (b) 5 # 8 (c) 11 # 9

First, divide to 2 decimalplaces. Then round off youranswer to 1 decimal place.

(8) Divide. Round off your answer to the nearest hundredth (2 decimal places).

(a) 3 # 7 (b) 13 # 6

!""""8 7 !"""""9 1 1

!""""7 3 6 1 3!""""""

!""""8 50 .87

07 06 4

60564

0.9

8 ! 12= 20

$3 ! $7= $10

$9 ! $20= $29

22 " 12= 10

36 " 15= 21

$15 " $6= $9

1.2

1 . 2 2

92 01 8

2 01 8

2

0 . 4 28

03 02 8

2 01 4

6 05 6

4

0.43 2.17

2 . 1 66

1 21 0

6 4 036

4036

4

0 . 62

05 04 8

2 01 6

4

0.6

Chapter 10: Decimals (2) Chapter 10: Decimals (2)60 61

(3) Estimate the value of each of the following:

(a) 0.47 ! 15.51

(b) 9.95 " 1.46

(c) 2.89 cm # 4

(d) 6.34 kg $ 7

(2) Estimate the product or quotient.

(a) 4.5 # 4 (b) 19.6 # 3

(c) 0.95 # 8 (d) 24.6 $ 5

(e) 72.09 $ 8 (f) 99.75 $ 5

0.5 ! 15.5= 16

10.0 " 1.5= 8.5

3 # 4= 12 cm

6.3 $ 7= 0.9 kg

5 # 4= 20

20 # 3= 60

1 # 8= 8

25 $ 5= 5

72 $ 8= 9

100 $ 5= 20


Name: Class: Date:


Practice 8 Word Problems(1) How many litres of cola are there in 6 similar cans if each can contains

0.33 ! of cola? Round off your answer to the nearest litre.

(2) A plumber cut a length of copper pipe into 4 equal pieces. The pipe was0.9 m long. Find the length of each piece in metres. Round off your answerto 1 decimal place.

(3) Meilin is thinking of a number. When she divides it by 7, she gets 7.35.What number is Meilin thinking of?

(4) A packet of potato chips is sold at $1.95. Estimate the cost of 8 suchpackets of potato chips.

(5) A piece of plywood is 1.27 cm thick. Estimate the thickness of a pile of9 such pieces of plywood.

0.33 # 6= 1.98 2

There are about 2 ! of cola in 6 similar cans.

0.9 $ 4 = 0.225 0.2

The length of each piece was about 0.2 m.

7.35 # 7 = 51.45

Meilin is thinking of 51.45.

1.95 $28 # $2 = $16

The cost of 8 such packets of potato chips is about $16.

1.27 11 # 9 = 9

The thickness of a pile of 9 such pieces of plywood is about 9 cm.


Name: Class: Date:


Practice 8 Word Problems(1) How many litres of cola are there in 6 similar cans if each can contains

0.33 ! of cola? Round off your answer to the nearest litre.

(2) A plumber cut a length of copper pipe into 4 equal pieces. The pipe was0.9 m long. Find the length of each piece in metres. Round off your answerto 1 decimal place.

(3) Meilin is thinking of a number. When she divides it by 7, she gets 7.35.What number is Meilin thinking of?

(4) A packet of potato chips is sold at $1.95. Estimate the cost of 8 suchpackets of potato chips.

(5) A piece of plywood is 1.27 cm thick. Estimate the thickness of a pile of9 such pieces of plywood.

0.33 ! 6= 1.98 2

There are about 2 ! of cola in 6 similar cans.

0.9 " 4 = 0.225 0.2

The length of each piece was about 0.2 m.

7.35 ! 7 = 51.45

Meilin is thinking of 51.45.

1.95 $28 ! $2 = $16

The cost of 8 such packets of potato chips is about $16.

1.27 11 ! 9 = 9

The thickness of a pile of 9 such pieces of plywood is about 9 cm.


(7) A sack contains 10 kg of rice. A family uses 0.85 kg of rice a day. How muchrice is left in the sack after 7 days? Give your answer to the nearest kilogram.

(8) A packet of rice crackers costs $1.95. What is the greatest number of packetsof rice crackers Ajay can buy with $10.00?

(4) 2 kg of milk powder cost $13.70. Find the cost of 6 kg of milk powder.

(5) 3 cans of cola cost $1.80. Rizal bought 9 cans of cola. How much did hehave to pay?

(6) During the school holidays, Andrew worked for 6 days each week. He workedthe same number of hours each day. He was paid $5.00 an hour. In a week, heearned $225. How many hours a day did he work?

0.85 # 7 = 5.9510 " 5.95 = 4.05

4

About 4 kg of rice is left in the sack after 7 days.

$1.95 $210 $ 2 = 5

The greatest number of packets of rice crackers Ajay can buy with $10.00is 5.

$225 $ 6 = $37.50$37.50 $ $5 = 7.5

He worked 7.5 hours a day.

$13.70 $ 2 = $6.85$6.85 # 6 = $41.10

The cost of 6 kg of milk powder is $41.10.

$1.80 $ 3 = $0.60$0.60 # 9 = $5.40

He had to pay $5.40.


(7) A sack contains 10 kg of rice. A family uses 0.85 kg of rice a day. How muchrice is left in the sack after 7 days? Give your answer to the nearest kilogram.

(8) A packet of rice crackers costs $1.95. What is the greatest number of packetsof rice crackers Ajay can buy with $10.00?

(4) 2 kg of milk powder cost $13.70. Find the cost of 6 kg of milk powder.

(5) 3 cans of cola cost $1.80. Rizal bought 9 cans of cola. How much did hehave to pay?

(6) During the school holidays, Andrew worked for 6 days each week. He workedthe same number of hours each day. He was paid $5.00 an hour. In a week, heearned $225. How many hours a day did he work?

0.85 ! 7 = 5.9510 " 5.95 = 4.05

4

About 4 kg of rice is left in the sack after 7 days.

$1.95 $210 # 2 = 5

The greatest number of packets of rice crackers Ajay can buy with $10.00is 5.

$225 # 6 = $37.50$37.50 # $5 = 7.5

He worked 7.5 hours a day.

$13.70 # 2 = $6.85$6.85 ! 6 = $41.10

The cost of 6 kg of milk powder is $41.10.

$1.80 # 3 = $0.60$0.60 ! 9 = $5.40

He had to pay $5.40.


Challenging Practice

Name: Class: Date:


(1) 3 cups and 2 bowls can hold a total of 2.88 ! of water. A bowl can hold 3times as much water as a cup. Find how much water a bowl can hold.

(2) Yani is 4.5 kg lighter than Lili. Rina is twice as heavy as Yani. The total mass ofthe three girls is 142.1 kg. What is Yanis mass?

(9) A metal rod 9.4 m long is cut into two pieces. One piece is 3 times as longas the other. Find the length of the longer piece in metres. Round off youranswer to 1 decimal place.

(10) Rani bought 9 similar exercise books. She gave the cashier $10.00 andreceived a change of $5.05. What was the cost of 1 exercise book?

9.4 $ 4 = 2.352.35 # 3 = 7.05

7.1

The length of the longer piece is about 7.1 m.bowls

cups2.88 !

Lili

Yani 142.1 kg

Rina

4.5 kg

9 units 2.88 !1 unit 2.88 $ 9 = 0.32 !3 # 0.32 = 0.96

A bowl can hold 0.96 ! of water.

4 units 142.1 " 4.5 = 137.6 kg1 unit 137.6 $ 4 = 34.4 kg

Yanis mass is 34.4 kg.

$10 " $5.05 = $4.95$4.95 $ 9 = $0.55

The cost of 1 exercise book was $0.55.


Challenging Practice

Name: Class: Date:


(1) 3 cups and 2 bowls can hold a total of 2.88 ! of water. A bowl can hold 3times as much water as a cup. Find how much water a bowl can hold.

(2) Yani is 4.5 kg lighter than Lili. Rina is twice as heavy as Yani. The total mass ofthe three girls is 142.1 kg. What is Yanis mass?

(9) A metal rod 9.4 m long is cut into two pieces. One piece is 3 times as longas the other. Find the length of the longer piece in metres. Round off youranswer to 1 decimal place.

(10) Rani bought 9 similar exercise books. She gave the cashier $10.00 andreceived a change of $5.05. What was the cost of 1 exercise book?

9.4 ! 4 = 2.352.35 " 3 = 7.05

7.1

The length of the longer piece is about 7.1 m.bowls

cups2.88 !

Lili

Yani 142.1 kg

Rina

4.5 kg

9 units 2.88 !1 unit 2.88 ! 9 = 0.32 !3 " 0.32 = 0.96

A bowl can hold 0.96 ! of water.

4 units 142.1 # 4.5 = 137.6 kg1 unit 137.6 ! 4 = 34.4 kg

Yanis mass is 34.4 kg.

$10 # $5.05 = $4.95$4.95 ! 9 = $0.55

The cost of 1 exercise book was $0.55.

Problem Solving

Name: Class: Date:


(1) The numbers in two circles on a line add up to the number in the squarebetween the circles. Find the missing numbers.

A

1.4

1.7B

0.9

C

(2) Gillian bought some buns and cakes for $15.25. A bun and a cake cost $2together and each cake cost $1.25. If she bought one more cake than buns,how many buns did she buy?

Start with the sum 0.9 since it is the smallest. Try 0.1 ! 0.8.Putting 0.1 in A and 0.8 in C will give B = 1.7 " 0.8 = 0.9, but 0.9 ! 0.1 = 1,which is less than 1.4. This implies that a larger number should be put in A.Try 0.3 in A and 0.6 in C. This will give B = 1.7 " 0.6 = 1.1 and 1.1 ! 0.3 isequal to 1.4. Therefore, A = 0.3, B= 1.1 and C = 0.6.

$15.25 " $1.25 = $1414 $ 2 = 7

She bought 7 buns.

0.3

1.1 0.6

4b workbook answers (prac 7

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