MENTAL ARITHMETIC: MULTIPLICATION PROBLEMS To see the answer, pass your mouse over the colored area. 1. a) 3 × 4 cm. What does that mean? 4 cm + 4 cm + 4 cm. 1. a) What is 3 called? The multiplier. 1. a) What is 4 cm called? The multiplicand. 1. b) 4 × 3 cm. What does that mean? 3 cm + 3 cm + 3 cm + 3 cm. 1. b) Which is the multiplicand? 3 cm. 1. b) What is 4 called? The multiplier. 2. a) Five 7's are what multiplication? 5 × 7 2. b) Six eights are what multiplication? 6 × 8 3. According to the order property of multiplication: Nine 6's = Six 9's. 4. The order of factors. Multiply mentally. 4. a) 2 × 9 × 6 × 5 = 10 × 54 = 540 4. b) 7 × 25 × 8 × 4 = 100 × 56 = 5600 4. c) 2 × 2 × 2 × 3 × 5 × 5 × 7 = (2 × 2 × 5 × 5) × 2 × 3 × 7 = 100 × 42 = 4200 5. When numbers are repeatedly added, we obtain their multiples. Write 5. a) 25. 25, 50, 75, 100, 125, 150. 5. b) 12. (To go to each next multiple of 12: 12 = 10 + 2.
5. c) 35. 35, 70, 105, 140, 175. 5. d) 75. 75, 150, 225, 300, 375, 450. 5. e) 18. (To go to each next multiple of 18: 18 = 20 − 2.
6. Whole numbers that end in 0's. Calculate mentally. 6. a) 3 × 60 = 180 b) 30 × 600 = 18,000 6. c) 300 × 6000 = 1,800,000 5. d) 9 × 50 = 450 e) 40 × 7 = 280 f) 60 × 8 = 480 5. g) 250 × 300 = 75,000 h) 2000 × 1200 = 2,400,000 5. i) 700 × 700 = 490,000 j) 3,000 × 15,000 = 45,000,000 7. Calculate mentally. 7. a) 6 × $.40 = $2.40 b) 7 × $.30 = $2.10 c) 8 × $.60 = $4.80 6. d) 9 × $.70 = $6.30 e) 5 × $.80 = $4.00 f) 4 × $.50  = $2.00 8. Expanding into units. Calculate in writing by expanding the 8. a) 15 × 3. (10 threes + 5 threes) = 30 + 15 = 45. 8. b) 14 × 7 = Ten 7's + Four 7's = 70 + 28 = 98 8. c) 17 × 9 = Ten 9's + Seven 9's = 90 + 63 = 153 8. d) 32 × 6 = 180 + 12 = 192 8. e) 11 × 53 = 530 + 53 = 583
11. Calculate mentally. 10. a) 27 × 3 = 60 + 21 = 81 10. b) 32 × 6 = 180 + 12 = 192 10. c) 45 × 5 = 200 + 25 = 225 10. d) 64 × 9 = 540 + 36 = 576
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