MENTAL ARITHMETIC: MULTIPLICATION

PROBLEMS (2)

The distributive property

Do the problem yourself first!

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

13.  a)  3 × 42

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

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

13.  d)  7 × 56 = 350 + 42 = 392

13.  e)  8 × 97 = 720 + 56 = 776

13.  f)  2 × 346 = 600 + 80 + 12 = 692

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

13.  h)  7 × 908 = 6300 + 56 = 6,356

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

13.  j)  6 × 7.30 = 42 + 1.80 = 43.80

13.  k)  9 × 4.50 = 36 + 4.50 = 40.50

14.  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

15.  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

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

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

17.  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

18.  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 × 2009 = 10,045

Continue on to the next section.

or