Primary 5 Mathematics Decimals Quiz

Primary 5 Mathematics Quiz - Decimals (Answer Key)

Total Marks: 50

Section A: Multiple Choice Questions (10 marks)

2 marks each. Award 1 mark for correct method if final answer is wrong.

1. B) 7 hundredths

• Explanation: In the number 3.072, the digits are: 3 (ones), 0 (tenths), 7 (hundredths), 2 (thousandths). The digit 7 is in the hundredths place.
• Marking: 2 marks for correct answer.

2. B) 0.80

• Explanation: Adding a zero at the end of a decimal does not change its value. 0.8 = 0.80. The other options are different values: 0.08 is eight hundredths, 8.0 is eight, and 80.0 is eighty.
• Marking: 2 marks for correct answer.

3. B) 5.7

• Explanation: To round 5.689 to 1 decimal place, look at the digit in the second decimal place (hundredths), which is 8. Since 8 ≥ 5, we round up the first decimal place (tenths) from 6 to 7. So, 5.689 rounded to 1 decimal place is 5.7.
• Marking: 2 marks for correct answer.

4. D) 50

• Explanation: Multiplying a decimal by 100 moves the decimal point two places to the right. 0.5 × 100 = 50.
• Marking: 2 marks for correct answer.

5. B) 0.102

• Explanation: Compare the decimals by looking at the digits from left to right.
  • 0.12 = 0.120
  • 0.102 = 0.102
  • 0.21 = 0.210
  • 0.201 = 0.201 The smallest is 0.102.
• Marking: 2 marks for correct answer.

Section B: Short Answer Questions (20 marks)

2 marks each. Award 1 mark for correct method if final answer is wrong.

6. 0.35

• Explanation: To convert a fraction to a decimal, divide the numerator by the denominator. 7 ÷ 20 = 0.35. Alternatively, find an equivalent fraction with a denominator of 100: $\frac{7}{20} = \frac{7 \times 5}{20 \times 5} = \frac{35}{100} = 0.35$.
• Marking: 2 marks for correct answer. 1 mark for correct method but wrong answer.

7. 0.54, 0.504, 0.45, 0.405

• Explanation: Write all numbers with the same number of decimal places: 0.450, 0.405, 0.540, 0.504. Compare the tenths digit first. 0.540 and 0.504 have 5 tenths, so they are larger. 0.540 > 0.504. Then compare 0.450 and 0.405. 0.450 > 0.405. So the order from largest is: 0.54, 0.504, 0.45, 0.405.
• Marking: 2 marks for correct order. 1 mark for partially correct order.

8. 0.42

• Explanation: Multiply the numbers as if they were whole numbers: 6 × 7 = 42. Count the total number of decimal places in the factors: 0.6 has 1 decimal place, 0.7 has 1 decimal place. Total = 2 decimal places. Place the decimal point in the product so that it has 2 decimal places: 0.42.
• Marking: 2 marks for correct answer. 1 mark for correct method but wrong answer.

9. 0.5 m

• Explanation: Divide the total length by the number of pieces: 2.5 ÷ 5 = 0.5. Each piece is 0.5 m long.
• Marking: 2 marks for correct answer with unit. 1 mark for correct method but wrong answer.

10. 6.25

• Explanation: Align the decimal points and add: 3.45 + 2.80 = 6.25.
• Marking: 2 marks for correct answer. 1 mark for correct method but wrong answer.

11. 3.45

• Explanation: Align the decimal points and subtract: 4.70 - 1.25 = 3.45.
• Marking: 2 marks for correct answer. 1 mark for correct method but wrong answer.

12. 1500 ml

• Explanation: 1 litre = 1000 millilitres. So, 1.5 litres = 1.5 × 1000 = 1500 millilitres.
• Marking: 2 marks for correct answer with unit. 1 mark for correct method but wrong answer.

13. 0.84

• Explanation: Dividing by 10 moves the decimal point one place to the left. 8.4 ÷ 10 = 0.84.
• Marking: 2 marks for correct answer. 1 mark for correct method but wrong answer.

14. 2.75 m

• Explanation: Subtract the length cut off from the original length: 3.6 - 0.85 = 2.75. The remaining cloth is 2.75 m long.
• Marking: 2 marks for correct answer with unit. 1 mark for correct method but wrong answer.

15. $\frac{3}{4}$

• Explanation: 0.75 is read as "seventy-five hundredths", which is $\frac{75}{100}$. Simplify the fraction by dividing the numerator and denominator by their greatest common factor, 25: $\frac{75 \div 25}{100 \div 25} = \frac{3}{4}$.
• Marking: 2 marks for correct answer in simplest form. 1 mark for $\frac{75}{100}$ without simplification.

Section C: Problem Sums (20 marks)

4 marks each. Award marks for correct method and working.

16. 27.5 kg

• Explanation:
  1. Mass of sack = 10 × 2.5 kg = 25 kg
  2. Total mass = 2.5 kg + 25 kg = 27.5 kg
• Marking:
  • 1 mark for finding mass of sack (25 kg)
  • 2 marks for finding total mass (27.5 kg)
  • 1 mark for correct unit (kg)
  • Award 2 marks for correct method but wrong answer.

17. 8 cakes

• Explanation:
  1. Number of cakes = Total flour ÷ Flour per cake
  2. Number of cakes = 3.6 ÷ 0.45
  3. To divide by a decimal, multiply both numbers by 100: 360 ÷ 45 = 8
• Marking:
  • 2 marks for correct division setup (3.6 ÷ 0.45)
  • 2 marks for correct answer (8)
  • Award 2 marks for correct method but wrong answer.

18. 1.6 m

• Explanation:
  1. Length of second piece = 1.2 m + 0.8 m = 2.0 m
  2. Total length of first and second pieces = 1.2 m + 2.0 m = 3.2 m
  3. Length of third piece = 4.8 m - 3.2 m = 1.6 m
• Marking:
  • 1 mark for finding length of second piece (2.0 m)
  • 1 mark for finding total of first two pieces (3.2 m)
  • 2 marks for finding length of third piece (1.6 m)
  • Award 2 marks for correct method but wrong answer.

19. 11.05 litres

• Explanation:
  1. Water after pouring = 12.5 litres + 3.75 litres = 16.25 litres
  2. Water left after using = 16.25 litres - 5.2 litres = 11.05 litres
• Marking:
  • 2 marks for finding water after pouring (16.25 litres)
  • 2 marks for finding water left (11.05 litres)
  • Award 2 marks for correct method but wrong answer.

20. $4.90

• Explanation:
  1. Cost of 6 apples = 6 × $0.85 =$5.10
  2. Change = $10.00 -$5.10 = $4.90
• Marking:
  • 2 marks for finding cost of apples ($5.10)
  • 2 marks for finding change ($4.90)
  • Award 2 marks for correct method but wrong answer.