Primary 4 Mathematics · Chapter 10 · Answers and explanations
Lesson 10.1: Addition of Decimals (answers) Section A · Multiple choice 4 marks 1. 3.4 + 5.3 = ?1 mark
(A) 8.07 (B) 2.1 (C) 8.7 (D) 87
Answer: (C) 8.7 Add the tenths: 4 + 3 = 7. Add the ones: 3 + 5 = 8. So 3.4 + 5.3 = 8.7.
2. 4.26 + 3.51 = ?1 mark
(A) 7.67 (B) 8.77 (C) 0.777 (D) 7.77
Answer: (D) 7.77 Hundredths: 6 + 1 = 7. Tenths: 2 + 5 = 7. Ones: 4 + 3 = 7. So 7.77.
3. 7.6 + 2.8 = ?1 mark
(A) 10.4 (B) 9.14 (C) 10.14 (D) 9.4
Answer: (A) 10.4 6 tenths + 8 tenths = 14 tenths, write 4 and carry 1. 7 + 2 + 1 = 10. So 10.4.
4. 2.9 + 4.75 = ?1 mark
(A) 7.15 (B) 7.65 (C) 6.65 (D) 7.4
Answer: (B) 7.65 Write 2.9 as 2.90. Hundredths: 0 + 5 = 5. Tenths: 9 + 7 = 16, write 6 and carry 1. Ones: 2 + 4 + 1 = 7. So 7.65.
Section B · Write your answer 11 marks 5. 2.7 + 6.2 = ______1 mark
Answer: 8.9 Tenths: 7 + 2 = 9. Ones: 2 + 6 = 8. So 8.9.
6. 5.08 + 3.41 = ______1 mark
Answer: 8.49 Hundredths: 8 + 1 = 9. Tenths: 0 + 4 = 4. Ones: 5 + 3 = 8. So 8.49.
7. 4.9 + 3.6 = ______1 mark
Answer: 8.5 9 tenths + 6 tenths = 15 tenths, write 5 and carry 1. 4 + 3 + 1 = 8. So 8.5.
8. 3.67 + 2.85 = ______1 mark
Answer: 6.52 Hundredths: 7 + 5 = 12, write 2 carry 1. Tenths: 6 + 8 + 1 = 15, write 5 carry 1. Ones: 3 + 2 + 1 = 6. So 6.52.
9. 15.8 + 4.35 = ______2 marks
Answer: 20.15 Write 15.8 as 15.80. Then 15.80 + 4.35 = 20.15.
10. 9.48 + 0.52 = ______1 mark
Answer: 10 Hundredths: 8 + 2 = 10, carry 1. Tenths: 4 + 5 + 1 = 10, carry 1. Ones: 9 + 0 + 1 = 10. So 10.00 = 10.
11. 36.4 + 7.89 = ______2 marks
Answer: 44.29 Write 36.4 as 36.40. Then 36.40 + 7.89 = 44.29.
12. A rope is 12.35 m long. Another rope is 8.9 m long. What is the total length of the two ropes?2 marks
Answer: 21.25 m Add: 12.35 + 8.90 = 21.25. The total length is 21.25 m.
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Primary 4 Mathematics · Chapter 10 · Answers and explanations
Lesson 10.2: Subtraction of Decimals (answers) Section A · Multiple choice 4 marks 1. 8.6 − 3.4 = ?1 mark
(A) 5.02 (B) 12 (C) 4.2 (D) 5.2
Answer: (D) 5.2 Tenths: 6 − 4 = 2. Ones: 8 − 3 = 5. So 5.2.
2. 7.45 − 2.31 = ?1 mark
(A) 5.14 (B) 5.24 (C) 4.14 (D) 5.16
Answer: (A) 5.14 Hundredths: 5 − 1 = 4. Tenths: 4 − 3 = 1. Ones: 7 − 2 = 5. So 5.14.
3. 6.3 − 2.7 = ?1 mark
(A) 4.6 (B) 3.6 (C) 4.4 (D) 3.4
Answer: (B) 3.6 3 tenths − 7 tenths cannot be done. Rename 1 one as 10 tenths: 13 − 7 = 6. Ones: 5 − 2 = 3. So 3.6.
4. 9.02 − 3.57 = ?1 mark
(A) 6.55 (B) 5.55 (C) 5.45 (D) 6.45
Answer: (C) 5.45 Rename across the zero: 9.02 = 8 ones 9 tenths 12 hundredths. 12 − 7 = 5, 9 − 5 = 4, 8 − 3 = 5. So 5.45.
Section B · Write your answer 11 marks 5. 9.8 − 4.5 = ______1 mark
Answer: 5.3 Tenths: 8 − 5 = 3. Ones: 9 − 4 = 5. So 5.3.
6. 8.75 − 3.42 = ______1 mark
Answer: 5.33 Hundredths: 5 − 2 = 3. Tenths: 7 − 4 = 3. Ones: 8 − 3 = 5. So 5.33.
7. 7.2 − 3.9 = ______1 mark
Answer: 3.3 2 tenths − 9 tenths cannot be done. Rename: 12 − 9 = 3. Ones: 6 − 3 = 3. So 3.3.
8. 6.14 − 2.78 = ______1 mark
Answer: 3.36 Rename: 14 − 8 = 6 hundredths. Tenths 0 after renaming, rename again: 10 − 7 = 3. Ones: 5 − 2 = 3. So 3.36.
9. 10 − 3.6 = ______2 marks
Answer: 6.4 Write 10 as 10.0. 10.0 − 3.6 = 6.4.
10. 8 − 2.45 = ______1 mark
Answer: 5.55 Write 8 as 8.00. 8.00 − 2.45 = 5.55.
11. 52.3 − 17.86 = ______2 marks
Answer: 34.44 Write 52.3 as 52.30. 52.30 − 17.86 = 34.44.
12. A tank holds 25 ℓ of water. 8.75 ℓ are used. How much water is left?2 marks
Answer: 16.25 ℓ 25.00 − 8.75 = 16.25. There are 16.25 ℓ left.
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Primary 4 Mathematics · Chapter 10 · Answers and explanations
Lesson 10.3: Word Problems: Adding and Subtracting (answers) Section A · Multiple choice 4 marks 1. Nina walks 3.25 km to the park and then 1.8 km to the library. How far does she walk in all?1 mark
(A) 5.05 km (B) 1.45 km (C) 5.43 km (D) 4.43 km
Answer: (A) 5.05 km Add the parts: 3.25 + 1.80 = 5.05. She walks 5.05 km.
2. Ben has $12.60. He spends $4.35. How much money does he have left?1 mark
(A) $16.95 (B) $8.25 (C) $8.35 (D) $7.25
Answer: (B) $8.25 Subtract: 12.60 − 4.35 = 8.25. He has $8.25 left.
3. Ribbon A is 7.5 m long. It is 2.25 m longer than Ribbon B. How long is Ribbon B?1 mark
(A) 9.75 m (B) 5.35 m (C) 5.25 m (D) 4.25 m
Answer: (C) 5.25 m Ribbon B is shorter, so subtract: 7.50 − 2.25 = 5.25. Ribbon B is 5.25 m long.
4. A pumpkin has a mass of 4.8 kg. A melon has a mass of 6.35 kg. How much heavier is the melon?1 mark
(A) 11.15 kg (B) 2.55 kg (C) 1.45 kg (D) 1.55 kg
Answer: (D) 1.55 kg Compare, so subtract: 6.35 − 4.80 = 1.55. The melon is 1.55 kg heavier.
Section B · Write your answer 11 marks 5. Two bags have masses of 2.45 kg and 3.8 kg. What is their total mass?1 mark
Answer: 6.25 kg Add: 2.45 + 3.80 = 6.25. The total mass is 6.25 kg.
6. A jug had 3.5 ℓ of juice. 1.75 ℓ were poured out. How much juice is left?1 mark
Answer: 1.75 ℓ Subtract: 3.50 − 1.75 = 1.75. There is 1.75 ℓ left.
7. A book costs $8.90 and a pen costs $2.65. What is the total cost?1 mark
Answer: $11.55 Add: 8.90 + 2.65 = 11.55. The total cost is $11.55.
8. Tom pays $20 for a toy that costs $13.45. How much change does he get?1 mark
Answer: $6.55 Subtract: 20.00 − 13.45 = 6.55. His change is $6.55.
9. A train ride is 12.6 km. A bus ride is 4.75 km longer than the train ride. How long is the bus ride?1 mark
Answer: 17.35 km Longer, so add: 12.60 + 4.75 = 17.35. The bus ride is 17.35 km.
10. Sara has 18.5 m of cloth. She uses 6.75 m for curtains and 4.9 m for cushions. How much cloth is left?2 marks
Answer: 6.85 m Cloth used: 6.75 + 4.90 = 11.65. Cloth left: 18.50 − 11.65 = 6.85. She has 6.85 m left.
11. Amy has a mass of 14.25 kg. Bob is 3.6 kg lighter than Amy. What is the total mass of Amy and Bob?2 marks
Answer: 24.9 kg Bob: 14.25 − 3.60 = 10.65 kg. Total: 14.25 + 10.65 = 24.90. The total mass is 24.9 kg.
12. A tank holds 10 ℓ. Wayne pours in 2.85 ℓ and then 4.76 ℓ of water. How much more water is needed to fill the tank?2 marks
Answer: 2.39 ℓ Water poured in: 2.85 + 4.76 = 7.61. Water needed: 10.00 − 7.61 = 2.39. He needs 2.39 ℓ more.
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Primary 4 Mathematics · Chapter 10 · Answers and explanations
Lesson 10.4: Multiplication of Decimals (answers) Section A · Multiple choice 4 marks 1. 0.4 × 3 = ?1 mark
(A) 12 (B) 1.2 (C) 0.12 (D) 7
Answer: (B) 1.2 4 tenths × 3 = 12 tenths = 1.2.
2. 2.3 × 4 = ?1 mark
(A) 8.12 (B) 8.2 (C) 9.2 (D) 92
Answer: (C) 9.2 3 tenths × 4 = 12 tenths: write 2, carry 1. 2 × 4 = 8, plus 1 = 9. So 9.2.
3. 3.06 × 5 = ?1 mark
(A) 15.03 (B) 1.53 (C) 153 (D) 15.3
Answer: (D) 15.3 6 hundredths × 5 = 30 hundredths: write 0, carry 3 tenths. 0 × 5 + 3 = 3 tenths. 3 × 5 = 15. So 15.30 = 15.3.
4. 4.28 × 3 = ?1 mark
(A) 12.84 (B) 12.24 (C) 13.84 (D) 128.4
Answer: (A) 12.84 8 × 3 = 24: write 4, carry 2. 2 × 3 = 6, plus 2 = 8. 4 × 3 = 12. So 12.84.
Section B · Write your answer 11 marks 5. 0.05 × 8 = ______1 mark
Answer: 0.4 5 hundredths × 8 = 40 hundredths = 0.40 = 0.4.
6. 0.7 × 6 = ______1 mark
Answer: 4.2 7 tenths × 6 = 42 tenths = 4.2.
7. 5.4 × 3 = ______1 mark
Answer: 16.2 4 × 3 = 12: write 2, carry 1. 5 × 3 = 15, plus 1 = 16. So 16.2.
8. 6.25 × 4 = ______1 mark
Answer: 25 5 × 4 = 20: write 0, carry 2. 2 × 4 = 8, plus 2 = 10: write 0, carry 1. 6 × 4 = 24, plus 1 = 25. So 25.00 = 25.
9. 12.6 × 5 = ______1 mark
Answer: 63 6 × 5 = 30: write 0, carry 3. 2 × 5 = 10, plus 3 = 13: write 3, carry 1. 1 × 5 = 5, plus 1 = 6. So 63.0 = 63.
10. 3.48 × 9 = ______2 marks
Answer: 31.32 8 × 9 = 72: write 2, carry 7. 4 × 9 = 36, plus 7 = 43: write 3, carry 4. 3 × 9 = 27, plus 4 = 31. So 31.32.
11. 45.07 × 6 = ______2 marks
Answer: 270.42 7 × 6 = 42, write 2 carry 4. 0 × 6 + 4 = 4. 5 × 6 = 30, write 0 carry 3. 4 × 6 = 24, plus 3 = 27. So 270.42.
12. Each pack of cards costs $4.85. How much do 6 packs cost?2 marks
Answer: $29.10 4.85 × 6 = 29.10. The cost is $29.10.
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Primary 4 Mathematics · Chapter 10 · Answers and explanations
Lesson 10.5: Division of Decimals (answers) Section A · Multiple choice 4 marks 1. 0.8 ÷ 2 = ?1 mark
(A) 4 (B) 0.04 (C) 0.4 (D) 0.2
Answer: (C) 0.4 8 tenths ÷ 2 = 4 tenths = 0.4.
2. 4.8 ÷ 3 = ?1 mark
(A) 16 (B) 1.2 (C) 0.16 (D) 1.6
Answer: (D) 1.6 4 ones ÷ 3 = 1 one remainder 1. 1 one 8 tenths = 18 tenths. 18 tenths ÷ 3 = 6 tenths. So 1.6.
3. 7.5 ÷ 5 = ?1 mark
(A) 1.5 (B) 15 (C) 1.05 (D) 0.15
Answer: (A) 1.5 7 ones ÷ 5 = 1 one remainder 2. 2 ones 5 tenths = 25 tenths. 25 ÷ 5 = 5 tenths. So 1.5.
4. 9.12 ÷ 4 = ?1 mark
(A) 2.82 (B) 2.28 (C) 2.38 (D) 22.8
Answer: (B) 2.28 9 ÷ 4 = 2 remainder 1. 11 tenths ÷ 4 = 2 remainder 3. 32 hundredths ÷ 4 = 8. So 2.28.
Section B · Write your answer 11 marks 5. 0.06 ÷ 2 = ______1 mark
Answer: 0.03 6 hundredths ÷ 2 = 3 hundredths = 0.03.
6. 8.4 ÷ 6 = ______1 mark
Answer: 1.4 8 ÷ 6 = 1 remainder 2. 24 tenths ÷ 6 = 4 tenths. So 1.4.
7. 5.04 ÷ 7 = ______1 mark
Answer: 0.72 0 ones. 50 tenths ÷ 7 = 7 tenths remainder 1. 14 hundredths ÷ 7 = 2 hundredths. So 0.72.
8. 3 ÷ 4 = ______1 mark
Answer: 0.75 3 ÷ 4 = 0 remainder 3. 30 tenths ÷ 4 = 7 tenths remainder 2. 20 hundredths ÷ 4 = 5. So 0.75.
9. 17 ÷ 5 = ______1 mark
Answer: 3.4 17 ÷ 5 = 3 remainder 2. 20 tenths ÷ 5 = 4 tenths. So 3.4.
10. 36.4 ÷ 8 = ______2 marks
Answer: 4.55 36 ÷ 8 = 4 remainder 4. 44 tenths ÷ 8 = 5 remainder 4. 40 hundredths ÷ 8 = 5. So 4.55.
11. 5 ÷ 6 = ______ (correct to 1 decimal place)2 marks
Answer: 0.8 5 ÷ 6 = 0.833... The 2nd decimal place is 3, so round down. 0.8.
12. 10 ÷ 3 = ______ (correct to 2 decimal places)2 marks
Answer: 3.33 10 ÷ 3 = 3.333... The 3rd decimal place is 3, so round down. 3.33.
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Primary 4 Mathematics · Chapter 10 · Answers and explanations
Lesson 10.6: Word Problems: Multiplying and Dividing (answers) Section A · Multiple choice 4 marks 1. A book costs $3.85. How much do 4 books cost?1 mark
(A) $12.40 (B) $7.85 (C) $154 (D) $15.40
Answer: (D) $15.40 Equal groups, so multiply: 3.85 × 4 = 15.40. They cost $15.40.
2. A 7.5 m rope is cut into 5 equal pieces. How long is each piece?1 mark
(A) 1.5 m (B) 2.5 m (C) 0.15 m (D) 15 m
Answer: (A) 1.5 m Divide: 7.5 ÷ 5 = 1.5. Each piece is 1.5 m.
3. Mia buys 6 bottles of juice. Each bottle holds 1.25 ℓ. How much juice does she buy?1 mark
(A) 6.25 ℓ (B) 7.5 ℓ (C) 7.25 ℓ (D) 75 ℓ
Answer: (B) 7.5 ℓ Multiply: 1.25 × 6 = 7.50. She buys 7.5 ℓ.
4. 18.6 kg of sand is shared equally among 3 boxes. How much sand is in each box?1 mark
(A) 62 kg (B) 5.2 kg (C) 6.2 kg (D) 6.02 kg
Answer: (C) 6.2 kg Divide: 18.6 ÷ 3 = 6.2. Each box has 6.2 kg.
Section B · Write your answer 11 marks 5. Eight pencils cost $0.65 each. How much do they cost altogether?1 mark
Answer: $5.20 0.65 × 8 = 5.20. They cost $5.20.
6. A 12.8 m wire is cut into 4 equal pieces. How long is each piece?1 mark
Answer: 3.2 m 12.8 ÷ 4 = 3.2. Each piece is 3.2 m.
7. Bag A has a mass of 2.45 kg. Bag B is 3 times as heavy as Bag A. What is the mass of Bag B?1 mark
Answer: 7.35 kg 2.45 × 3 = 7.35. Bag B has a mass of 7.35 kg.
8. A packet holds 0.75 kg of rice. How much rice is in 6 packets?1 mark
Answer: 4.5 kg 0.75 × 6 = 4.50. There is 4.5 kg of rice.
9. $54.60 is shared equally among 7 children. How much does each child get?1 mark
Answer: $7.80 54.60 ÷ 7 = 7.80. Each child gets $7.80.
10. Mr Roy buys 5 pens at $2.40 each. He pays with a $20 note. How much change does he get?2 marks
Answer: $8 Cost: 2.40 × 5 = 12.00. Change: 20 − 12 = 8. His change is $8.
11. Peter’s rope is 4 times as long as Sam’s rope. Together the two ropes are 15.5 m long. How long is Peter’s rope?2 marks
Answer: 12.4 m Sam = 1 unit, Peter = 4 units, together 5 units = 15.5 m. 1 unit = 15.5 ÷ 5 = 3.1 m. Peter: 4 × 3.1 = 12.4 m.
12. Ali saves $3.75 each week for 8 weeks. He then spends $12.50. How much money does he have left?2 marks
Answer: $17.50 Saved: 3.75 × 8 = 30.00. Left: 30.00 − 12.50 = 17.50. He has $17.50.
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Primary 4 Mathematics · Chapter 10 · Answers and explanations
Chapter 10 Revision Paper: Four Operations of Decimals (answers) Section A · Multiple choice 10 marks 1. 3.45 + 2.8 = ?1 mark
(A) 3.73 (B) 5.25 (C) 6.53 (D) 6.25
Answer: (D) 6.25 Line up the decimal points: write 2.8 as 2.80. Hundredths: 5 + 0 = 5. Tenths: 4 + 8 = 12 tenths, write 2 and regroup 1 one. Ones: 3 + 2 + 1 = 6. The answer is 6.25.
2. 0.678 + 1.9 = ?1 mark
(A) 2.578 (B) 1.578 (C) 0.697 (D) 2.687
Answer: (A) 2.578 Write 1.9 as 1.900 so the decimal points line up. Thousandths: 8. Hundredths: 7 + 0 = 7. Tenths: 6 + 9 = 15 tenths, write 5 and regroup 1 one. Ones: 0 + 1 + 1 = 2. The answer is 2.578.
3. 7.2 − 3.46 = ?1 mark
(A) 4.46 (B) 3.74 (C) 3.86 (D) 4.26
Answer: (B) 3.74 Write 7.2 as 7.20. Hundredths: 0 − 6 is not possible, so regroup 1 tenth as 10 hundredths: 10 − 6 = 4. Tenths: 1 − 4 is not possible, so regroup 1 one: 11 − 4 = 7. Ones: 6 − 3 = 3. The answer is 3.74.
4. 5 − 2.37 = ?1 mark
(A) 3.63 (B) 2.73 (C) 2.63 (D) 3.37
Answer: (C) 2.63 Write 5 as 5.00. Regroup across the zeros: 5.00 is 4 ones, 9 tenths and 10 hundredths. Hundredths: 10 − 7 = 3. Tenths: 9 − 3 = 6. Ones: 4 − 2 = 2. The answer is 2.63.
5. A red rope is 8.4 m long. A blue rope is 2.75 m shorter than the red rope. How long is the blue rope?1 mark
(A) 11.15 m (B) 6.35 m (C) 5.75 m (D) 5.65 m
Answer: (D) 5.65 m The blue rope is shorter, so subtract: 8.40 − 2.75 = 5.65. The blue rope is 5.65 m long.
6. 0.6 × 7 = ?1 mark
(A) 4.2 (B) 42 (C) 0.42 (D) 4.7
Answer: (A) 4.2 6 tenths × 7 = 42 tenths. 42 tenths = 4 ones and 2 tenths = 4.2.
7. 3.06 × 4 = ?1 mark
(A) 12.024 (B) 12.24 (C) 12.4 (D) 1.224
Answer: (B) 12.24 Multiply from the right. Hundredths: 6 × 4 = 24, write 4 and carry 2 tenths. Tenths: 0 × 4 = 0, plus 2 = 2. Ones: 3 × 4 = 12. The answer is 12.24.
8. 0.37 × 100 = ?1 mark
(A) 3.7 (B) 370 (C) 37 (D) 3700
Answer: (C) 37 Multiplying by 100 makes the number 100 times as great. Each digit moves 2 places to the left: 0.37 becomes 37.
9. 7.35 ÷ 3 = ?1 mark
(A) 2.5 (B) 2.05 (C) 24.5 (D) 2.45
Answer: (D) 2.45 7 ones ÷ 3 = 2 ones remainder 1. 13 tenths ÷ 3 = 4 tenths remainder 1. 15 hundredths ÷ 3 = 5 hundredths. So the answer is 2.45.
10. $26.40 is shared equally among 8 children. How much does each child get?1 mark
(A) $3.30 (B) $3.03 (C) $0.33 (D) $33.00
Answer: (A) $3.30 26.40 ÷ 8: 26 ones ÷ 8 = 3 ones remainder 2. 24 tenths ÷ 8 = 3 tenths. 0 hundredths ÷ 8 = 0. So each child gets $3.30.
Section B · Short answers 4 marks 11. 12.4 + 5.76 = ______1 mark
Answer: 18.16 Write 12.4 as 12.40. Hundredths: 0 + 6 = 6. Tenths: 4 + 7 = 11, write 1 and regroup 1 one. Ones: 2 + 5 + 1 = 8. Tens: 1. The answer is 18.16.
12. 10 − 6.085 = ______1 mark
Answer: 3.915 Write 10 as 10.000 and regroup across the zeros: 10.000 is 9 ones, 9 tenths, 9 hundredths and 10 thousandths. Thousandths: 10 − 5 = 5. Hundredths: 9 − 8 = 1. Tenths: 9 − 0 = 9. Ones: 9 − 6 = 3. The answer is 3.915.
13. 12.75 × 6 = ______1 mark
Answer: 76.5 Hundredths: 5 × 6 = 30, write 0 and carry 3. Tenths: 7 × 6 = 42, plus 3 = 45, write 5 and carry 4. Ones: 2 × 6 = 12, plus 4 = 16, write 6 and carry 1. Tens: 1 × 6 = 6, plus 1 = 7. So 76.50 = 76.5.
14. 19.32 ÷ 6 = ______1 mark
Answer: 3.22 19 ones ÷ 6 = 3 ones remainder 1. 13 tenths ÷ 6 = 2 tenths remainder 1. 12 hundredths ÷ 6 = 2 hundredths. The answer is 3.22.
Section C · Show your working 16 marks 15. Lina buys a bag for $12.80 and a hat for $7.45. She pays with a $50 note. How much change does she get?2 marks
Money $12.80 $7.45 $29.75 $50 Answer: $29.75 Total cost: 12.80 + 7.45 = 20.25. Change: 50 − 20.25 = 29.75. She gets $29.75 change.
16. Rope A is 6.4 m long. Rope B is 1.85 m shorter than Rope A. What is the total length of the two ropes?2 marks
Rope A 6.4 m Rope B 4.55 m 1.85 m
Answer: 10.95 m Rope B: 6.40 − 1.85 = 4.55 m. Total: 6.40 + 4.55 = 10.95. The two ropes are 10.95 m long altogether.
17. Each bottle holds 1.35 ℓ of juice. How much juice is there in 6 such bottles?2 marks
Juice 1.35 ℓ 1.35 ℓ 1.35 ℓ 1.35 ℓ 1.35 ℓ 1.35 ℓ 8.1 ℓ Answer: 8.1 ℓ 6 equal bottles, so multiply: 1.35 × 6. Hundredths: 5 × 6 = 30, write 0, carry 3. Tenths: 3 × 6 = 18, plus 3 = 21, write 1, carry 2. Ones: 1 × 6 = 6, plus 2 = 8. So 8.10 = 8.1. There is 8.1 ℓ of juice.
18. A 14.4 m ribbon is cut into 8 equal pieces. Mrs Ong uses 3 of the pieces. What is the total length of the pieces she uses?2 marks
Ribbon 1.8 m 1.8 m 1.8 m 1.8 m 1.8 m 1.8 m 1.8 m 1.8 m 14.4 m Answer: 5.4 m One piece: 14.4 ÷ 8 = 1.8 m (14 ones ÷ 8 = 1 one remainder 6; 64 tenths ÷ 8 = 8 tenths). Three pieces: 1.8 × 3 = 5.4 m. She uses 5.4 m.
19. Fish costs $9.65 per kg. Mr Lim buys 4 kg of fish and pays with a $50 note. How much change does he get?2 marks
Fish $9.65 $9.65 $9.65 $9.65 Paid $50 $38.60 Answer: $11.40 Cost of fish: 9.65 × 4 = 38.60. Change: 50 − 38.60 = 11.40. He gets $11.40 change.
20. A notebook costs $3.50. The notebook and 5 identical pens cost $11.25 altogether. What is the cost of one pen?2 marks
Total $3.50 $1.55 $1.55 $1.55 $1.55 $1.55 $11.25 Answer: $1.55 Cost of the 5 pens: 11.25 − 3.50 = 7.75. Cost of 1 pen: 7.75 ÷ 5 = 1.55 (7 ones ÷ 5 = 1 one remainder 2; 27 tenths ÷ 5 = 5 tenths remainder 2; 25 hundredths ÷ 5 = 5 hundredths). One pen costs $1.55.
21. Bag A is 3 times as heavy as Bag B. Bag A is 7.2 kg heavier than Bag B. What is the total mass of the two bags?2 marks
Bag B 3.6 kg Bag A 3.6 kg 3.6 kg 3.6 kg 7.2 kg Answer: 14.4 kg Bag B is 1 unit and Bag A is 3 units. The difference is 3 − 1 = 2 units, and 2 units = 7.2 kg. 1 unit = 7.2 ÷ 2 = 3.6 kg. Together there are 1 + 3 = 4 units: 4 × 3.6 = 14.4. The total mass is 14.4 kg.
22. Dev has 4 times as much money as Eli. Dev gives Eli $9.60. Then they have the same amount of money. How much money did Dev have at first?2 marks
Dev $6.40 $6.40 $6.40 Eli $6.40 gives $9.60 Answer: $25.60 At first Dev has 4 units and Eli has 1 unit, so Dev has 3 units more than Eli (3 units). When Dev gives Eli $9.60, Dev loses $9.60 and Eli gains $9.60, so the difference changes by 2 × $9.60 = $19.20. They are now equal, so 3 units = $19.20. 1 unit = 19.20 ÷ 3 = $6.40. Dev: 4 × 6.40 = $25.60. Check: Dev has 25.60 − 9.60 = $16 and Eli has 6.40 + 9.60 = $16.
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