Primary 4 Mathematics · Chapter 2 · Answers and explanations
Lesson 2.5: Common Multiples (answers)
Section A · Multiple choice 4 marks
1. Which of these is a common multiple of 4 and 6?1 mark
(A) 12(B) 8(C) 18(D) 16
Answer: (A) 1212 is in the 4 times table (4 × 3) and in the 6 times table (6 × 2). 8 and 16 are only multiples of 4. 18 is only a multiple of 6.
2. What is the first common multiple of 6 and 8?1 mark
(A) 48(B) 24(C) 14(D) 12
Answer: (B) 24Multiples of 6: 6, 12, 18, 24. Multiples of 8: 8, 16, 24. The first number in both lists is 24. (48 is a common multiple, but not the first.)
3. Some multiples of 4 and of 10 are listed. What is the first common multiple of 4 and 10?1 mark
(A) 40(B) 8(C) 20(D) 14
Answer: (C) 2020 is the first number that appears in both lists. 40 is also in both lists, but it comes later.
4. Which of these is NOT a common multiple of 4 and 6?1 mark
(A) 12(B) 24(C) 36(D) 30
Answer: (D) 3012, 24 and 36 are all in both the 4 times table and the 6 times table. 30 is a multiple of 6 but 30 ÷ 4 leaves a remainder.
Section B · Write your answer 11 marks
5. Find the first common multiple of 5 and 7.1 mark
Answer: 35Multiples of 5: 5, 10, 15, 20, 25, 30, 35. Multiples of 7: 7, 14, 21, 28, 35. The first number in both lists is 35.
6. Find the first common multiple of 9 and 12.1 mark
Answer: 36Multiples of 9: 9, 18, 27, 36. Multiples of 12: 12, 24, 36. The first number in both lists is 36.
7. Find the first common multiple of 10 and 15.1 mark
Answer: 30Multiples of 10: 10, 20, 30. Multiples of 15: 15, 30. The first number in both lists is 30.
8. Find the first common multiple of 6 and 12.1 mark
Answer: 12Multiples of 6: 6, 12. Multiples of 12: 12. The first number in both lists is 12, because 12 is itself a multiple of 6.
9. List all the common multiples of 4 and 6 that are less than 50.1 mark
Answer: 12, 24, 36, 48The first common multiple is 12. The other common multiples are multiples of 12: 12, 24, 36, 48.
10. A red bus leaves a bus stop every 6 minutes. A blue bus leaves the same stop every 8 minutes. Both buses leave together at 9:00 a.m. At what time will they next leave together?2 marks
Answer: 9:24 a.m.Find the first common multiple of 6 and 8. Multiples of 6: 6, 12, 18, 24. Multiples of 8: 8, 16, 24. It is 24, so the buses leave together again 24 minutes after 9:00 a.m., at 9:24 a.m.
11. Pencils are sold in packs of 6 and erasers in packs of 4. Ravi wants to buy the same number of pencils and erasers. What is the least number of each he can buy? How many packs of each does he buy?2 marks
Answer: 12 of each; 2 packs of pencils and 3 packs of erasersThe first common multiple of 6 and 4 is 12, so he buys 12 pencils and 12 erasers. Pencils: 12 ÷ 6 = 2 packs. Erasers: 12 ÷ 4 = 3 packs.
12. Ali visits the library every 3 days. Ben visits the library every 4 days. They both visit on a Monday. On which day of the week will they next visit on the same day?2 marks
Answer: SaturdayThe first common multiple of 3 and 4 is 12, so they meet again after 12 days. 12 days = 1 week and 5 days. 5 days after Monday is Saturday.
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