Primary 4 Mathematics Decimals Quiz

Primary 4 Mathematics Quiz - Decimals: Answer Key

Total Marks: 40

Section A: Multiple-Choice Questions (5 questions x 2 marks = 10 marks)

1. Answer: B) 7 hundredths

• Marks: 2
• Explanation: In the number 3.075, the digit 7 is in the hundredths place. The place values after the decimal point are: tenths (0.1), hundredths (0.01), thousandths (0.001). So, 7 is in the hundredths place, meaning it represents 7 hundredths or 0.07.
• Common Mistake: Students might confuse hundredths with thousandths. The digit 5 is in the thousandths place.

2. Answer: C) 0.5

• Marks: 2
• Explanation: To compare decimals, align them by place value:
  • 0.5 = 0.500
  • 0.45 = 0.450
  • 0.405 = 0.405
  • 0.054 = 0.054 Comparing the tenths place: 0.5 has 5 tenths, which is the largest. 0.45 and 0.405 have 4 tenths, and 0.054 has 0 tenths.
• Common Mistake: Students might think 0.45 is larger than 0.5 because 45 is larger than 5, forgetting to compare place values.

3. Answer: B) 0.7

• Marks: 2
• Explanation: $\frac{7}{10}$ means 7 tenths. In decimal form, this is written as 0.7. The first digit after the decimal point represents tenths.
• Common Mistake: Students might write 0.07, confusing tenths with hundredths.

4. Answer: A) 4.8

• Marks: 2
• Explanation: To round 4.836 to 1 decimal place, we look at the digit in the second decimal place (hundredths), which is 3. Since 3 is less than 5, we round down, meaning the digit in the first decimal place (tenths) stays the same. So, 4.836 rounded to 1 decimal place is 4.8.
• Common Mistake: Students might round up because they see 36, forgetting to only look at the digit immediately to the right of the rounding place.

5. Answer: B) $\frac{6}{100}$

• Marks: 2
• Explanation: 0.06 is read as "six hundredths". The digit 6 is in the hundredths place. Therefore, it is equal to $\frac{6}{100}$.
• Common Mistake: Students might choose $\frac{6}{10}$ (0.6) or $\frac{60}{100}$ (0.60).

Section B: Short-Answer Questions (10 questions x 2 marks = 20 marks)

6. Answer: 0.37

• Marks: 2 (1 mark for correct method, 1 mark for correct answer)
• Explanation: The diagram is a 10x10 grid, which represents 100 equal parts. 37 squares are shaded. This represents 37 out of 100, or $\frac{37}{100}$, which is written as the decimal 0.37.
• Marking Note: Accept 0.37 or $\frac{37}{100}$.

7. Answer: 0.208, 0.28, 0.802, 0.82

• Marks: 2 (1 mark for correct order, but not starting with the smallest)
• Explanation: To compare, write them with the same number of decimal places:
  • 0.82 = 0.820
  • 0.28 = 0.280
  • 0.802 = 0.802
  • 0.208 = 0.208 Now compare the digits from left to right. The smallest is 0.208 (0 tenths), then 0.280 (2 tenths), then 0.802 (8 tenths), then 0.820 (8 tenths, but 0.802 has 0 hundredths while 0.820 has 2 hundredths, so 0.802 is smaller).
• Common Mistake: Students might order by the number of digits (e.g., putting 0.82 before 0.802).

8. Answer: 8.25

• Marks: 2 (1 mark for correct method, 1 mark for correct answer)
• Explanation: Align the decimal points and add:

    5.90
  + 2.35
  ------
    8.25
  

• Working: 5.9 + 2.35 = 5.90 + 2.35 = 8.25

9. Answer: 4.72

• Marks: 2 (1 mark for correct method, 1 mark for correct answer)
• Explanation: Align the decimal points and subtract:

    6.20
  - 1.48
  ------
    4.72
  

• Working: 6.2 - 1.48 = 6.20 - 1.48 = 4.72

10. Answer: 20.4

• Marks: 2 (1 mark for correct method, 1 mark for correct answer)
• Explanation: Multiply 3.4 by 6 as if it were a whole number (34 x 6 = 204). Since 3.4 has 1 decimal place, the answer must also have 1 decimal place. So, 204 becomes 20.4.
• Working: 3.4 x 6 = 20.4

11. Answer: 1.2

• Marks: 2 (1 mark for correct method, 1 mark for correct answer)
• Explanation: Divide 8.4 by 7. 7 goes into 8 once, with 1 remainder. Bring down the 4 to make 14. 7 goes into 14 twice. Place the decimal point directly above the decimal point in the dividend. So, 8.4 ÷ 7 = 1.2.
• Working: 8.4 ÷ 7 = 1.2

12. Answer: 0.6

• Marks: 2 (1 mark for correct method, 1 mark for correct answer)
• Explanation: To express $\frac{3}{5}$ as a decimal, find an equivalent fraction with a denominator of 10. Multiply the numerator and denominator by 2: $\frac{3}{5} = \frac{3 \times 2}{5 \times 2} = \frac{6}{10} = 0.6$.
• Alternative Method: Divide the numerator by the denominator: 3 ÷ 5 = 0.6.

13. Answer: 12.68

• Marks: 2 (1 mark for correct method, 1 mark for correct answer)
• Explanation: To round 12.679 to 2 decimal places, we look at the digit in the third decimal place (thousandths), which is 9. Since 9 is greater than or equal to 5, we round up the digit in the second decimal place (hundredths) from 7 to 8. So, 12.679 rounded to 2 decimal places is 12.68.
• Common Mistake: Students might forget to round up the 7 to 8.

14. Answer: 40

• Marks: 2
• Explanation: Multiplying a decimal by 100 moves the decimal point two places to the right. 0.4 x 100 = 40. (0.4 → 04.0 → 40)
• Common Mistake: Students might think the answer is 0.400 or 400.

15. Answer: 0.5 m

• Marks: 2 (1 mark for correct method, 1 mark for correct answer)
• Explanation: The ribbon is 2.5 m long and is cut into 5 equal pieces. To find the length of each piece, divide 2.5 by 5. 2.5 ÷ 5 = 0.5. Each piece is 0.5 m long.
• Working: 2.5 ÷ 5 = 0.5

Section C: Problem-Solving Questions (5 questions x 2 marks = 10 marks)

16. Answer: 2.25 litres

• Marks: 2 (1 mark for correct method, 1 mark for correct answer)
• Explanation: To find the total amount of water, add the amounts in both bottles. 1.5 + 0.75 = 2.25 litres.
• Working: 1.50 + 0.75 = 2.25

17. Answer: 1.75 m

• Marks: 2 (1 mark for correct method, 1 mark for correct answer)
• Explanation: To find the amount of cloth left, subtract the amount used from the original length. 3.6 - 1.85 = 1.75 m.
• Working: 3.60 - 1.85 = 1.75

18. Answer: 2 kg

• Marks: 2 (1 mark for correct method, 1 mark for correct answer)
• Explanation: To find the total mass of 8 packets, multiply the mass of one packet by 8. 0.25 x 8 = 2 kg.
• Working: 0.25 x 8 = 2.00 = 2

19. Answer: 0.4 litres

• Marks: 2 (1 mark for correct method, 1 mark for correct answer)
• Explanation: To find the amount of juice in each glass, divide the total amount of juice by the number of glasses. 2.4 ÷ 6 = 0.4 litres.
• Working: 2.4 ÷ 6 = 0.4

20. Answer: $4.90

• Marks: 2 (1 mark for correct method, 1 mark for correct answer)
• Explanation:
  1. Find the cost of the pen: $1.20 + $2.50 = $3.70
  2. Find the total cost: $1.20 + $3.70 = $4.90
• Working:
  • Pen: $1.20 + $2.50 = $3.70
  • Total: $1.20 + $3.70 = $4.90