Primary 4 Mathematics Decimals Quiz

Primary 4 Mathematics Quiz - Decimals - Answer Key

Total Marks: 30

Section A: Multiple Choice Questions (Questions 1 to 5)

1.

• Answer: (3) 7 thousandths
• Marks: 1
• Explanation: In the number 3.207, the digits after the decimal point represent tenths, hundredths, and thousandths. The digit 7 is in the third place after the decimal, which is the thousandths place. So, its value is 7 thousandths.
• Common Mistake: Students often confuse the place values after the decimal point. The first place is tenths, the second is hundredths, and the third is thousandths.

2.

• Answer: (3) 0.55
• Marks: 1
• Explanation: To compare decimals, we can look at the digits in each place value. All numbers have 0 in the ones place. In the tenths place, 0.5, 0.55, and 0.505 have 5, while 0.05 has 0. So, 0.05 is the smallest. For the remaining three, we look at the hundredths place: 0.5 has 0, 0.55 has 5, and 0.505 has 0. So, 0.55 is the largest.
• Common Mistake: Students might think 0.505 is larger than 0.55 because it has more digits. They need to compare digit by digit from left to right.

3.

• Answer: (2) 0.7
• Marks: 1
• Explanation: The fraction $\frac{7}{10}$ means 7 tenths. In decimal form, this is written as 0.7.
• Common Mistake: Students might write 0.07, confusing tenths with hundredths.

4.

• Answer: (1) 4.8
• Marks: 1
• 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 do not round up the digit in the first decimal place (tenths), which is 8. So, the answer is 4.8.
• Common Mistake: Students might round up because they see the digit 3 and think it's closer to 5, but the rule is to round up only if the digit is 5 or more.

5.

• Answer: (3) 5.55
• Marks: 1
• Explanation: Align the decimal points and add: $3.45 + 2.10 = 5.55$.
• Common Mistake: Students might forget to align the decimal points and add 3.45 + 2.1 as 3.45 + 2.1 = 3.66.

Section B: Short Answer Questions (Questions 6 to 15)

6.

• Answer: 0.08, 0.8, 0.808, 0.88
• Marks: 2 (1 mark for correct order, 1 mark for all correct)
• Explanation: Compare the decimals digit by digit. All have 0 in the ones place. In the tenths place: 0.08 has 0, while the others have 8. So, 0.08 is the smallest. For the remaining three, compare the hundredths place: 0.8 has 0, 0.808 has 0, and 0.88 has 8. So, 0.88 is the largest. Now compare 0.8 and 0.808: 0.8 has 0 in the thousandths place, while 0.808 has 8. So, 0.8 is smaller than 0.808. The correct order is 0.08, 0.8, 0.808, 0.88.
• Common Mistake: Students might think 0.8 is the same as 0.80 and not consider the thousandths place.

7.

• Answer: $\frac{7}{20}$
• Marks: 2 (1 mark for correct fraction, 1 mark for simplification)
• Explanation: 0.35 is 35 hundredths, which is $\frac{35}{100}$. Simplify by dividing numerator and denominator by 5: $\frac{35 \div 5}{100 \div 5} = \frac{7}{20}$.
• Common Mistake: Students might forget to simplify the fraction.

8.

• Answer: 4.71
• Marks: 2 (1 mark for correct method, 1 mark for correct answer)
• Explanation: Align the decimal points and subtract: $5.60 - 0.89 = 4.71$.
• Common Mistake: Students might forget to regroup when subtracting.

9.

• Answer: 23.8
• Marks: 2 (1 mark for correct method, 1 mark for correct answer)
• Explanation: Multiply 34 by 7 to get 238. Since 3.4 has 1 decimal place, the answer should have 1 decimal place: 23.8.
• Common Mistake: Students might forget to place the decimal point in the answer.

10.

• Answer: 2.4
• Marks: 2 (1 mark for correct method, 1 mark for correct answer)
• Explanation: Divide 9.6 by 4: $9.6 \div 4 = 2.4$.
• Common Mistake: Students might forget to place the decimal point in the quotient.

11.

• Answer: 0.75 litres
• Marks: 2 (1 mark for correct method, 1 mark for correct answer and unit)
• Explanation: Subtract the amount drunk from the initial amount: $1.5 - 0.75 = 0.75$ litres.
• Common Mistake: Students might forget to align the decimal points.

12.

• Answer: 0.7 m
• Marks: 2 (1 mark for correct method, 1 mark for correct answer and unit)
• Explanation: Divide the total length by the number of pieces: $2.8 \div 4 = 0.7$ m.
• Common Mistake: Students might forget to place the decimal point in the quotient.

13.

• Answer: 12.35
• Marks: 2 (1 mark for correct method, 1 mark for correct answer)
• Explanation: To round 12.345 to 2 decimal places, we look at the digit in the third decimal place (thousandths), which is 5. Since it is 5 or more, we round up the digit in the second decimal place (hundredths), which is 4, to 5. So, the answer is 12.35.
• Common Mistake: Students might forget to round up when the digit is 5.

14.

• Answer: 0.6
• Marks: 2 (1 mark for correct method, 1 mark for correct answer)
• Explanation: $\frac{3}{5}$ is equivalent to $\frac{6}{10}$, which is 0.6.
• Common Mistake: Students might write 0.3 or 0.35.

15.

• Answer: 6.86
• Marks: 2 (1 mark for correct method, 1 mark for correct answer)
• Explanation: Align the decimal points and add: $2.30 + 4.56 = 6.86$.
• Common Mistake: Students might forget to align the decimal points.

Section C: Problem Sums (Questions 16 to 20)

16.

• Answer: 3.45 kg
• Marks: 3 (1 mark for correct method for sugar, 1 mark for correct method for flour, 1 mark for correct total)
• Explanation:
  • Weight of 3 packets of sugar: $3 \times 0.75 = 2.25$ kg
  • Weight of 2 packets of flour: $2 \times 0.6 = 1.2$ kg
  • Total weight: $2.25 + 1.2 = 3.45$ kg
• Common Mistake: Students might add the weights without multiplying by the number of packets.

17.

• Answer: 1.35 m
• Marks: 3 (1 mark for correct remaining length, 1 mark for correct division, 1 mark for correct answer and unit)
• Explanation:
  • Remaining cloth after cutting: $10 - 3.25 = 6.75$ m
  • Length of each piece: $6.75 \div 5 = 1.35$ m
• Common Mistake: Students might forget to subtract the curtain length first.

18.

• Answer: 4.45 kg
• Marks: 3 (1 mark for correct method, 1 mark for correct answer, 1 mark for correct unit)
• Explanation:
  • Mass of apples only: $4.8 - 0.35 = 4.45$ kg
• Common Mistake: Students might forget to align the decimal points.

19.

• Answer: 0.45 m
• Marks: 3 (1 mark for correct division, 1 mark for correct rounding, 1 mark for correct answer and unit)
• Explanation:
  • Length of each piece: $3.6 \div 8 = 0.45$ m
  • The answer is already correct to 2 decimal places.
• Common Mistake: Students might forget to round the answer.

20.

• Answer: 3.25 litres
• Marks: 3 (1 mark for correct method, 1 mark for correct answer, 1 mark for correct unit)
• Explanation:
  • Total water: $2.5 + 0.75 = 3.25$ litres
• Common Mistake: Students might forget to align the decimal points.

End of Answer Key