Primary 4 Mathematics · Chapter 1 · Answers and explanations
Chapter 1 Revision Paper: Numbers to 100 000 (answers)
Section A · Multiple choice 10 marks
1. Which number is seventy-three thousand and sixty-five?1 mark
(A) 73,650(B) 73,605(C) 73,065(D) 7,365
Answer: (C) 73,065Seventy-three thousand is 73,000. "Sixty-five" is 6 tens and 5 ones, so there are 0 hundreds. The number is 73,065.
2. Zara has 3 ten-thousand discs, 12 thousand discs, 5 hundred discs and 4 ones discs. What number do the discs show?1 mark
(A) 31,254(B) 42,054(C) 42,540(D) 42,504
Answer: (D) 42,5043 ten-thousands = 30,000 and 12 thousands = 12,000, so together they make 42,000. Add 500 and 4: 42,000 + 500 + 4 = 42,504.
3. What is the value of the digit 6 in 46,925?1 mark
(A) 6,000(B) 60,000(C) 600(D) 6
Answer: (A) 6,000The digit 6 is in the thousands place (4 is in the ten thousands, 6 in the thousands). So its value is 6,000.
4. Which number is the same as 50,000 + 300 + 7?1 mark
(A) 53,007(B) 50,307(C) 5,307(D) 50,370
Answer: (B) 50,307There are 5 ten thousands, 0 thousands, 3 hundreds, 0 tens and 7 ones. Write 0 in the empty places: 50,307.
5. Which number is greater than 63,508 but smaller than 63,580?1 mark
(A) 63,058(B) 63,805(C) 63,550(D) 63,508
Answer: (C) 63,550The numbers share 63, so compare the hundreds, then the tens. 63,550 has 5 hundreds and 5 tens, so it lies between 63,508 and 63,580. 63,058 is smaller; 63,805 is greater; 63,508 is not greater than itself.
6. What is the next number in the pattern? 19,850, 19,950, 20,050, ____1 mark
(A) 20,250(B) 21,050(C) 20,060(D) 20,150
Answer: (D) 20,150Each number is 100 more than the one before. 20,050 + 100 = 20,150. The hundreds digit goes from 0 to 1.
7. Round 6,995 to the nearest 10.1 mark
(A) 7,000(B) 6,990(C) 6,900(D) 7,100
Answer: (A) 7,000The ones digit is 5, so round up. 6,995 is halfway between 6,990 and 7,000, and we round up to 7,000.
8. Round 45,962 to the nearest 100.1 mark
(A) 45,900(B) 46,000(C) 45,960(D) 46,100
Answer: (B) 46,000Look at the tens digit: it is 6, so round up to the next hundred. 45,962 is between 45,900 and 46,000 and is nearer to 46,000.
9. Round 72,499 to the nearest 1000.1 mark
(A) 73,000(B) 72,500(C) 72,000(D) 72,400
Answer: (C) 72,000Look at the hundreds digit: it is 4, which is less than 5, so round down to 72,000. The last digits 99 do not change this.
10. Which number is 5,400 when rounded to the nearest 100?1 mark
(A) 5,451(B) 5,339(C) 5,550(D) 5,449
Answer: (D) 5,4495,449 has 4 tens, so round down to 5,400. 5,451 has 5 tens, so it rounds up to 5,500. 5,339 rounds to 5,300 and 5,550 rounds to 5,600.
Section B · Short answers 4 marks
11. Write the number: sixty-one thousand and eight.1 mark
Answer: 61,00861 thousands = 61,000. Then "eight" is 8 ones, so there are 0 hundreds and 0 tens. The number is 61,008.
12. Find the missing number. 41,300, 41,800, ____, 42,8001 mark
Answer: 42,30041,800 − 41,300 = 500, so the rule is add 500. 41,800 + 500 = 42,300. Check: 42,300 + 500 = 42,800.
13. Round 99,950 to the nearest 1000.1 mark
Answer: 100,000The hundreds digit is 9, so round up. 99,950 is closer to 100,000 than to 99,000. The answer is 100,000.
14. Use each of the digits 4, 0, 7, 2 and 9 once to make the smallest 5-digit number.1 mark
Answer: 20,479Put the smallest digits in the biggest places. The smallest digit is 0, but a 5-digit number cannot start with 0, so start with 2. Then 0, 4, 7, 9: 20,479.
Section C · Show your working 16 marks
15. Ravi has 4 ten-thousand discs, 15 thousand discs and 3 ten discs. What number do the discs show?2 marks
Answer: 55,03015 thousands = 10 thousands + 5 thousands, so regroup: 4 ten thousands + 1 ten thousand = 5 ten thousands. Now there are 5 ten thousands, 5 thousands, 0 hundreds, 3 tens and 0 ones. Or add: 40,000 + 15,000 + 30 = 55,030.
16. The digit 7 appears two times in 87,175. Find the difference between the greater value and the smaller value of the digit 7.2 marks
Answer: 6,930In 87,175, one 7 is in the thousands place, so its value is 7,000. The other 7 is in the tens place, so its value is 70. Difference: 7,000 − 70 = 6,930.
17. Write all the digits that can replace ■ so that 47,■85 < 47,385 is true.2 marks
Answer: 0, 1, 2The ten thousands and thousands are the same (47). Compare the hundreds: ■ must be less than 3. If ■ = 3, both numbers are 47,385, which is equal, not smaller. So ■ can be 0, 1 or 2.
18. The numbers of people living in four towns are: Town A: 38,405 Town B: 38,054 Town C: 83,045 Town D: 38,450 Arrange the towns from the town with the most people to the town with the fewest people.2 marks
Answer: C, D, A, BCompare the ten thousands first: Town C has 8 ten thousands, the others have 3, so C is greatest. For A, B and D (all 38,___), compare the hundreds: 38,450 and 38,405 have 4 hundreds, but 38,054 has 0. Then compare tens: 38,450 has 5 tens, 38,405 has 0 tens. Order: 83,045 > 38,450 > 38,405 > 38,054, so C, D, A, B.
19. Siti started to put numbers in this pattern. Find the rule. What is the first number in the pattern that is greater than 14,000?2 marks
Answer: 14,150The rule is add 350: 12,750 − 12,400 = 350. Keep adding: 13,450, 13,800 (not greater than 14,000), 14,150 (greater than 14,000). The first number is 14,150.
20. A stadium had 46,538 visitors on Saturday. Mei rounded the number to the nearest 1000. Ravi rounded it to the nearest 100. Find the difference between their answers.2 marks
21. A 4-digit number is 3,450 when rounded to the nearest 10 and 3,400 when rounded to the nearest 100. List all the numbers it could be.2 marks
Answer: 3,445; 3,446; 3,447; 3,448; 3,449To the nearest 10 it is 3,450, so it is from 3,445 to 3,454. To the nearest 100 it is 3,400, so it is from 3,350 to 3,449 (3,450 would round up to 3,500). Numbers in both lists: 3,445, 3,446, 3,447, 3,448 and 3,449.
22. Using each of the digits 3, 0, 7, 5 and 9 once, Ali forms the greatest 5-digit number and Mei forms the smallest 5-digit number. Round each number to the nearest 1000. Find the difference between the two rounded numbers.2 marks
Answer: 67,000Greatest: put the biggest digits first, 97,530. Smallest: 0 cannot be first, so 3, then 0, 5, 7, 9: 30,579. Round to the nearest 1000: 97,530 has 5 hundreds, round up to 98,000. 30,579 has 5 hundreds, round up to 31,000. Difference: 98,000 − 31,000 = 67,000.
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