Primary 4 Mathematics · Chapter 3 · Answers and explanations
Lesson 3.3: Multiplication by a 2-Digit Number (answers)
Section A · Multiple choice 4 marks
1. What is 53 × 20?1 mark
(A) 106(B) 10,600(C) 73(D) 1,060
Answer: (D) 1,060Multiply by 2 first: 53 × 2 = 106. Then multiply by 10 to make it × 20: 1,060.
2. What is 34 × 12?1 mark
(A) 408(B) 102(C) 68(D) 508
Answer: (A) 408Step 1 (ones): 34 × 2 = 68. Step 2 (tens): 34 × 10 = 340 (because 34 × 1 = 34, then × 10). Add: 68 + 340 = 408.
3. What is 215 × 14?1 mark
(A) 1,075(B) 3,010(C) 860(D) 3,110
Answer: (B) 3,010Step 1 (ones): 215 × 4 = 860. Step 2 (tens): 215 × 10 = 2,150 (because 215 × 1 = 215, then × 10). Add: 860 + 2,150 = 3,010.
4. What is 126 × 35?1 mark
(A) 1,008(B) 630(C) 4,410(D) 4,510
Answer: (C) 4,410Step 1 (ones): 126 × 5 = 630. Step 2 (tens): 126 × 30 = 3,780 (because 126 × 3 = 378, then × 10). Add: 630 + 3,780 = 4,410.
Section B · Write your answer 11 marks
5. What is 60 × 30?1 mark
Answer: 1,8006 × 3 = 18. There are two zeros in 60 × 30, so the answer is 1,800.
6. What is 47 × 13?1 mark
Answer: 611Step 1 (ones): 47 × 3 = 141. Step 2 (tens): 47 × 10 = 470 (because 47 × 1 = 47, then × 10). Add: 141 + 470 = 611.
7. What is 235 × 20?1 mark
Answer: 4,700235 × 2 = 470. Then × 10 gives 4,700.
8. What is 68 × 45?1 mark
Answer: 3,060Step 1 (ones): 68 × 5 = 340. Step 2 (tens): 68 × 40 = 2,720 (because 68 × 4 = 272, then × 10). Add: 340 + 2,720 = 3,060.
9. What is 312 × 24?1 mark
Answer: 7,488Step 1 (ones): 312 × 4 = 1,248. Step 2 (tens): 312 × 20 = 6,240 (because 312 × 2 = 624, then × 10). Add: 1,248 + 6,240 = 7,488.
10. A hall has 28 rows of chairs with 35 chairs in each row. 94 chairs are empty. How many chairs are used?2 marks
Answer: 886Chairs in the hall: 28 × 35. Step 1 (ones): 35 × 8 = 280. Step 2 (tens): 35 × 20 = 700 (because 35 × 2 = 70, then × 10). Add: 280 + 700 = 980. (Here 35 is multiplied by 8 and then by 20.) Chairs used: 980 − 94 = 886.
11. Mei reads 24 pages a day for 15 days. Her book has 400 pages. How many pages does she still have to read?2 marks
Answer: 40Pages read: 24 × 15 = 360 (24 × 5 = 120, 24 × 10 = 240, 120 + 240 = 360). Pages left: 400 − 360 = 40.
12. Ravi buys 32 packets of stickers at $15 each. He sells all the packets at $19 each. How much profit does he make?2 marks
Answer: $128Cost: 32 × 15 = 480 (32 × 5 = 160, 32 × 10 = 320). Sales: 32 × 19 = 608 (32 × 9 = 288, 32 × 10 = 320). Profit = $608 − $480 = $128.
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