MENTAL ARITHMETIC: MULTIPLICATION

PROBLEMS (2)

The distributive property

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13.  In this number  5,286  name the place value of each digit.

The 5 has the value 5000; the 2 signifies 200; the 8 signifies 80; and the 6 has its absolute value of 6.

14.  Calculate in writing by distributing the multiplier to each unit of the
12.  multiplicand.  Treat problems with decimal points as dollars and
14.  cents.

14.  a)  3 × 42

14.  b)  5 × 34 = 5 × 30 + 5 × 4 = 150 + 20 = 170

14.  c)  6 × 32 = 6 × 30 + 6 × 2 =180 + 12 = 192

14.  d)  7 × 56 = 350 + 42 = 392

14.  e)  8 × 97 = 720 + 56 = 776

14  f)  2 × 346 = 600 + 80 + 12 = 692

14.  g)  3 × 475 = 1200 + 210 + 15 = 1425

14.  h)  7 × 908 = 6300 + 56 = 6,356

14.  i)  9 × 4,005 = 36,000 + 45 = 36,045

13.  j)  6 × 7.30 = 42 + 1.80 = 43.80

14.  k)  9 × 4.50 = 36 + 4.50 = 40.50

15.  Whatever you wrote in the previous problem, do mentally here.

 6 × 13 = 78 7 × 55 = 385 3 × 96 = 288 3 × 72 = 216 9 × 72 = 648 5 × 68 = 340 8 × 34 =  272 8 × 36 =  288 6 × 36 =  216 4 × 49 =  196 6 × 89 =  534 4 × 38 =  152 9 × 52 =  468 8 × 28 =  224 9 × 36 =  324

16.  Calculate each column mentally.

 30 × 27 = 810 60 × 620 = 37,200 40 × 34 = 1360 70 × 770 = 53,900 50 × 59 = 2950 80 × 980 = 78,400

17.  You have 47 twenty-dollar bills.  Calculate mentally how much
17.  money you have.

2 × 47 = 80 + 14 = 94. Therefore 20 × 47 = \$940.

18.  Multiply each column mentally.  These are dollars and cents.

 4 × .25 = 1.00 6 × 3.25 = 19.50 7 × 9.50 = 66.50 5 × .25 = 1.25 5 × 6.25 = 31.25 3 × 4.80 = 14.40 6 × .25 = 1.50 6 × 9.25 = 55.50 9 × 5.20 = 46.80 7 × .25 = 1.75 7 × 8.25 = 57.75 4 × 6.30 = 25.20 8 × .25 = 2.00 8 × 4.25 = 34.00 7 × 7.40 = 51.80 9 × .25 = 2.25 9 × 5.25 = 47.25 8 × 3.90 = 31.20

19.  Multiply each column mentally by distributing the multiplier to the
18.  hundreds, then the tens, then the ones..

 2 × 423 = 846 7 × 309 = 2163 3 × 624 = 1872 8 × 602 = 4816 4 × 574 = 2296 9 × 907 = 8163 5 × 357 = 1785 5 × 2016  = 10,080

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