Chapter: 4th Maths : Term 3 Unit 2 : Numbers
Exercise 2.7 (multiplication facts by adding partial products mentally)
Numbers | Term 3 Chapter 2 | 4th Maths - Exercise 2.7
Exercise 2.7
Simplify the following multiplication facts by adding partial products.
1. \(9 \times 42\)
2. \(3 \times 78\)
3. \(36 \times 12\)
4. \(18 \times 19\)
5. \(68 \times 31\)
6. \(42 \times 21\)
Step-by-Step Solutions
1. \(9 \times 42\)
\(42 = 40 + 2\)
\(9 \times 40 = 360\)
\(9 \times 2 = 18\)
\(360 + 18 = 378\)
Answer: 378
2. \(3 \times 78\)
\(78 = 70 + 8\)
\(3 \times 70 = 210\)
\(3 \times 8 = 24\)
\(210 + 24 = 234\)
Answer: 234
3. \(36 \times 12\)
\(36 = 30 + 6\)
\(12 = 10 + 2\)
\(30 \times 10 = 300\)
\(30 \times 2 = 60\)
\(6 \times 10 = 60\)
\(6 \times 2 = 12\)
\(300 + 60 + 60 + 12 = 432\)
Answer: 432
4. \(18 \times 19\)
\(18 = 10 + 8\)
\(19 = 10 + 9\)
\(10 \times 10 = 100\)
\(10 \times 9 = 90\)
\(8 \times 10 = 80\)
\(8 \times 9 = 72\)
\(100 + 90 + 80 + 72 = 342\)
Answer: 342
5. \(68 \times 31\)
\(68 = 60 + 8\)
\(31 = 30 + 1\)
\(60 \times 30 = 1800\)
\(60 \times 1 = 60\)
\(8 \times 30 = 240\)
\(8 \times 1 = 8\)
\(1800 + 60 + 240 + 8 = 2108\)
Answer: 2108
6. \(42 \times 21\)
\(42 = 40 + 2\)
\(21 = 20 + 1\)
\(40 \times 20 = 800\)
\(40 \times 1 = 40\)
\(2 \times 20 = 40\)
\(2 \times 1 = 2\)
\(800 + 40 + 40 + 2 = 882\)
Answer: 882