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 the next multiple of 12, you could add 10 and then
5. c) 18. (To go to the next multiple of 18, you could add 20 and then
5. d) 35. 35, 70, 105, 140, 175, 210. 5. e) 75. 75, 150, 225, 300, 375, 450. 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. Decomposing the multiplier. Calculate in writing by decomposing 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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