SOLUTION: Mentally compute the product of 49 and 19. Describe the steps that you mentally went through to get your answer. Prove your answer using standard multiplication. Show your work.
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-> SOLUTION: Mentally compute the product of 49 and 19. Describe the steps that you mentally went through to get your answer. Prove your answer using standard multiplication. Show your work.
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Question 1084467: Mentally compute the product of 49 and 19. Describe the steps that you mentally went through to get your answer. Prove your answer using standard multiplication. Show your work. Found 2 solutions by ikleyn, Alan3354:Answer by ikleyn(52817) (Show Source):
Based on an identity (x-1)*(y-1) = xy - (x+y) + 1, substitute x= 50, y= 20 and do this:
1. Calculate 50*20 = 1000 (mentally).
2. Calculate 50 + 20 = 70 (mentally).
3. Subtract 70 from 1000 to get 930 (mentally).
4. Finally, add 1 to 930 to get 931 (mentally).
You can put this solution on YOUR website! Mentally compute the product of 49 and 19. Describe the steps that you mentally went through to get your answer.
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There's more than 1 way.
The average is (49+19)/2 = 34
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The difference from the average is 15
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49*19 = 34^2 - 15^2 = 1156 - 225 = 931
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Or,
50*19 = 950
950 - 19 = 931
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Or 49*19 = 7*7*19 = 7*133 = 931
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How is my way of doing it relevant?
How would you do it?
