MENTAL ARITHMETIC: MULTIPLICATION

PROBLEMS (3)

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  20.    Rounding off
 
  a)   Calculate in writing by distributing 2 to this difference:
 
  3 × (600 − 2) = 1800 − 6 = 1794
 
  b)   Multiply mentally:  3 × 598 = 1794

21.   Multiply each column mentally.  Treat problems with decimal points
21.   as dollars and cents.

6 × 99 = 594   2 × 2.95 = 5.90   7 × 11.98 = 83.86
 
5 × 79 = 395   3 × 4.95 = 14.85   5 × 16.96 = 84.80
 
3 × 89 =  267   6 × 5.98 = 35.88   7 × 24.98 =  174.86
 
8 × 39 =  312   5 × 7.99 =  39.95   3 × 19.95 =  59.85

Can you do these mentally, or with the least amount of writing?

22  At a political fund raising, fifty people paid $10,000 each to have
22. dinner with the President.  How much money was raised?  $500,000

23.  If your car gets 25 miles per gallon, how far could you go on 12
23 . gallons?  12 × 25 = 250 + 50 = 300 miles.

24.  What is the price of 4 airline tickets at $182 each?   $728

25.  What is the price of 6 airline tickets at $56.98 each?  $341.88

25.  What is the price of 60 tickets?  $3,418.80

26  If coffee sells for $3.95 a pound, what is the price of 4 pounds?
26.   $15.80

26.  What is the price of 40 pounds?  $158

27.  a)  How many days are there in 10 years?  Approximately 3,650.

27.  b)  How many days are there in 2 years?

27.   b) 2 × 365 = 600 + 120 + 10 = 730

27.  c)  How many days are there in 12 years?  3,650 + 730 = 4,380


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