Primary 2 Mathematics Numbers Quiz

Primary 2 Mathematics Quiz - Numbers: Answer Key (Version 1 of 5)

Total Marks: 50

Teaching notes are written for students new to the topic. Key idea: a 3-digit number has a hundreds digit, a tens digit and a ones digit; its value comes from the place of each digit.

Answer 1.

Answer: four hundred and sixty-eight (1 mark)

Teaching notes: Read the digits by place. $4$ is in the hundreds place, $6$ in the tens place, $8$ in the ones place, so we say "four hundred", then "sixty", then "eight". In Singapore we usually join them with "and": four hundred and sixty-eight. Common mistake: writing "four hundred sixty-eight" without "and" or mixing the tens and ones ("four hundred and eighty-six").

Answer 2.

Answer: $90$ (1 mark)

Method: Find the place of the digit $9$ in $392$. It stands in the tens place, so its value is $9$ tens $= 9 \times 10 = 90$. Common mistake: answering $9$, which is the digit itself, not its value. The value depends on the place, not just the digit.

Answer 3.

Answer: $<$ (1 mark)

Method: Compare place by place from the left. Hundreds: both are $7$, so they tie. Tens: $0$ is less than $8$. Therefore $708 < 780$. Teaching note: always start comparing at the largest place value.

Answer 4.

Answer: $340$ and $888$ (1 mark)

Teaching notes: An even number can be split into two equal groups; every even number ends in $0, 2, 4, 6$ or $8$. Only $340$ (ends in $0$) and $888$ (ends in $8$) qualify. $215$, $567$ and $901$ end in $5$, $7$ and $1$, so they are odd. Common mistake: looking at middle digits instead of the ones digit.

Answer 5.

Answer: $450$, $460$ (1 mark)

Method: The numbers go up by $10$ each time ($420 \to 430 \to 440$). Continue the rule: $440 + 10 = 450$, then $450 + 10 = 460$. Teaching note: name the rule first ("add 10"), then apply it.

Answer 6.

(a) $346$ (1 mark) (b) three hundred and forty-six (1 mark)

Expected visual: the figure must show exactly $3$ hundred-flats, $4$ ten-rods and $6$ unit cubes, labelled Hundreds/Tens/Ones.

Method: Count each group: $3$ flats $= 300$, $4$ rods $= 40$, $6$ cubes $= 6$. Add the place values: $300 + 40 + 6 = 346$. In words: three hundred and forty-six. Common mistake: reading the blocks as $3$,$4$,$6$ side by side without multiplying by the place values ($346$ happens to match here, but the counting-by-place method is what earns the mark).

Answer 7.

(a) $705$ (1 mark) (b) $990$ (1 mark)

Teaching notes: "Seven hundred and five" means $7$ hundreds, $0$ tens, $5$ ones, so the tens place must hold a $0$: $705$. Writing $75$ loses the mark because the zero keeps the places in line. "Nine hundred and ninety" means $9$ hundreds and $9$ tens with $0$ ones: $990$. Zero is a placeholder that holds an empty place.

Answer 8.

(a) $10$ (1 mark) (b) $864$ (1 mark)

Method (a): $517$ splits into $500 + 10 + 7$, so the missing tens part is $10$. Method (b): $800$ gives the hundreds digit $8$, $60$ gives the tens digit $6$, $4$ gives the ones digit $4$, giving $864$. Teaching note: expanded form shows the value hiding inside each digit.

Answer 9.

Answer: $590$, $580$ (2 marks)

Method: Counting backwards in tens means subtracting $10$ each time: $600 - 10 = 590$, then $590 - 10 = 580$, and indeed $580 - 10 = 570$ matches the last given number, confirming the rule. Marking: 1 mark per correct blank.

Answer 10.

Answer: Ravi is not correct. $347$ is an odd number. (2 marks)

Reasoning: Whether a number is even or odd depends only on its ones digit, not on any other digit. $347$ ends in $7$, and numbers ending in $1, 3, 5, 7, 9$ cannot be shared equally into two groups, so they are odd. The digit $4$ is in the tens place and tells us nothing about evenness. Marking: 1 mark for the correct decision, 1 mark for a valid explanation mentioning the ones digit.

Answer 11.

Answer: $569$, $596$, $659$, $695$ (3 marks)

Method: Compare the hundreds digits first. $569$ and $596$ have $5$ hundreds; $659$ and $695$ have $6$ hundreds, so the $5$-hundred numbers come first. Within each pair, compare the tens: $569$ has $6$ tens and $596$ has $9$ tens, so $569 < 596$; likewise $659 < 695$. Marking: 1 mark for correct grouping by hundreds, 1 mark for correct order within pairs, 1 mark for the fully correct sequence.

Answer 12.

Answer: $703$ (3 marks)

Step-by-step:

• Ones digit is given: $3$.
• Hundreds digit is $4$ more than the ones digit: $3 + 4 = 7$.

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# Primary 2 Mathematics Quiz - Numbers: Answer Key (Version 1 of 5)

**Total Marks: 50**

*Key idea: a 3-digit number has a hundreds digit, a tens digit and a ones digit; its value comes from the place of each digit.*

## Answer 1.
**Answer:** four hundred and sixty-eight **(1 mark)**

Notes: Read by place: $4$ hundreds, $6$ tens, $8$ ones. In Singapore we join with "and": *four hundred and sixty-eight*. Common mistake: swapping tens and ones ("eighty-six").

## Answer 2.
**Answer:** $90$ **(1 mark)**

Method: $9$ stands in the tens place of $392$, so its value is $9 \times 10 = 90$. Common mistake: answering $9$, which is the digit itself, not its value.

## Answer 3.
**Answer:** $<$ **(1 mark)**

Method: Compare from the left. Hundreds tie ($7 = 7$); tens: $0 < 8$. So $708 < 780$. Always start at the largest place value.

## Answer 4.
**Answer:** $340$ and $888$ **(1 mark)**

Notes: Even numbers end in $0, 2, 4, 6$ or $8$. Only $340$ (ends in $0$) and $888$ (ends in $8$) qualify. $215$, $567$, $901$ are odd. Common mistake: looking at middle digits instead of the ones digit.

## Answer 5.
**Answer:** $450$, $460$ **(1 mark)**

Method: Rule is add $10$: $440 + 10 = 450$, then $450 + 10 = 460$.

## Answer 6.
**(a)** $346$ **(1 mark)** **(b)** three hundred and forty-six **(1 mark)**

Expected visual: exactly $3$ hundred-flats, $4$ ten-rods, $6$ unit cubes, labelled Hundreds/Tens/Ones.

Method: Count by place: $3$ flats $= 300$, $4$ rods $= 40$, $6$ cubes $= 6$; $300 + 40 + 6 = 346$. In words: three hundred and forty-six.

## Answer 7.
**(a)** $705$ **(1 mark)** **(b)** $990$ **(1 mark)**

Notes: "Seven hundred and five" needs a $0$ in the tens place: $705$ (writing $75$ loses the mark). "Nine hundred and ninety" has $0$ ones: $990$. Zero holds an empty place.

## Answer 8.
**(a)** $10$ **(1 mark)** **(b)** $864$ **(1 mark)**

Method (a): $517 = 500 + 10 + 7$, so the missing part is $10$. Method (b): $800 \to 8$ hundreds, $60 \to 6$ tens, $4 \to 4$ ones gives $864$.

## Answer 9.
**Answer:** $590$, $580$ **(2 marks)**

Method: Backwards in tens means subtract $10$: $600 - 10 = 590$, $590 - 10 = 580$; check: $580 - 10 = 570$ matches the last number. 1 mark per blank.

## Answer 10.
**Answer:** Ravi is **not** correct; $347$ is an odd number. **(2 marks)**

Reasoning: Even or odd depends only on the **ones digit**. $347$ ends in $7$, and numbers ending in $1, 3, 5, 7, 9$ cannot be split into two equal groups, so they are odd. The digit $4$ is in the tens place and tells us nothing about evenness. Marking: 1 mark decision, 1 mark explanation mentioning the ones digit.

## Answer 11.
**Answer:** $569$, $596$, $659$, $695$ **(3 marks)**

Method: Compare hundreds first: $569$ and $596$ have $5$ hundreds, so they come before $659$ and $695$ ($6$ hundreds). Then compare tens within pairs: $569 < 596$ and $659 < 695$. Marking: 1 mark grouping by hundreds, 1 mark order within pairs, 1 mark full sequence.

## Answer 12.
**Answer:** $703$ **(3 marks)**

Steps:
- Ones digit given: $3$.
- Tens digit given: $0$.
- Hundreds digit is $4$ more than the ones digit: $3 + 4 = 7$.

So the number is $703$. Marking: 1 mark per correct digit found with working.

## Answer 13.
**Missing numbers:** $200$, $225$ **Rule:** add $25$ each time **(3 marks)**

Method: $125 \to 150 \to 175$ shows jumps of $25$. Continue: $175 + 25 = 200$, $200 + 25 = 225$. Marking: 1 mark per missing number, 1 mark for the rule.

## Answer 14.
**(a)** $<$ **(1 mark)** **(b)** $=$ **(1 mark)** **(c)** $=$ **(1 mark)**

Notes: (a) $609 < 690$ because $0$ tens $< 9$ tens. (b) $45$ tens $= 45 \times 10 = 450$, so equal. (c) $300 + 70 + 2 = 372$, so equal.

## Answer 15.
**Answer:** Dev, Cai, Amy, Ben **(3 marks)**

Method: Compare hundreds: Dev $583$ and Cai $538$ have $5$ hundreds, ahead of Amy $385$ and Ben $358$. Within pairs compare tens: $583 > 538$; $385 > 358$. So most to least: $583, 538, 385, 358$. Marking: 1 mark grouping, 1 mark within-pair order, 1 mark full sequence.

## Answer 16.
**(a)** $430$ **(1 mark)** **(b)** $470$ **(1 mark)** **(c)** $450$ **(2 marks)**

Method (c): Halfway between $430$ and $470$. Count steps: $430 \to 440 \to 450 \to 460 \to 470$ shows $450$ is $2$ steps from each end. Or $(430 + 470) \div 2 = 900 \div 2 = 450$. Marking: 1 mark answer, 1 mark valid working.

## Answer 17.
**(a)** $852$ **(2 marks)** **(b)** $285$ **(2 marks)**

Notes: (a) Greatest even: put the largest digit $8$ in front, next largest $5$ in the tens, leaving even digit $2$ last: $852$. It is even because it ends in $2$. (b) Only one odd digit ($5$) is available, so it must be the ones digit; put the smaller remaining digits first: $285$. It is odd because it ends in $5$. Marking: 1 mark number, 1 mark explanation each part.

## Answer 18.
**(a)** $375$, $475$, $575$, $675$ **(3 marks)** **(b)** $4$ hundreds ($400$) **(1 mark)**

Method: Counting on in hundreds adds $100$ each time: $275 + 100 = 375$, then $475$, $575$, $675$. Altogether she adds $4$ hundreds $= 400$.

## Answer 19.
**(a)** $471$, $295$ **(1 mark)** **(b)** $138$, $684$, $850$ **(2 marks)** **(c)** Look at the ones digit **(1 mark)**

Notes: (a) Odd numbers end in $1, 3, 5, 7, 9$: $471$ and $295$. (b) Even numbers end in $0, 2, 4, 6, 8$: order them by hundreds, then tens: $138 < 684 < 850$. (c) A number is even if its ones digit is $0, 2, 4, 6$ or $8$, and odd if its ones digit is $1, 3, 5, 7$ or $9$.

## Answer 20.
**Answer:** $653$ **(4 marks)**

Steps:
- Tens digit given: $5$.
- Ones digit is $2$ less than the tens digit: $5 - 2 = 3$.
- Hundreds digit is $3$ more than the ones digit: $3 + 3 = 6$.

Combine the digits: $6$ hundreds, $5$ tens, $3$ ones $\to 653$. Check: tens is $5$ ✓; ones is $2$ less than $5$ ✓; hundreds is $3$ more than $3$ ✓. Marking: 1 mark per correct step, 1 mark for the final number.

**End of Answer Key**