More On ShortCuts In Multiplication
66MORE ON SHORTCUTS IN MULTIPLICATION
Multiplying Two Numbers Whose Sum of Their Last Digits is 10 and Their Other Digits are the Same
Example One : 34 X 36
Solution by steps :
1) Multiply the first digit by one more than itself : 3 X 4 = 12
2) Multiply the last digits : 4 X 6 = 24
3) Combine the answer 1224
Short way : 3 X 4 = 12, 4 X 6 = 24 Answer: 34 X 36 = 1224
Multiplying Two 2-digit Numbers Whose Sum of Their First Digits is Ten and Their Last Digits are the Same
Example One : 64 X 44
Solution by steps :
1) Multiply the first digits and add a last digit: (6 X 4 ) = 24 + 4 = 28
2) Multiply the Last digits : 4 X 4 = 16
3) Combine : 2816
Short way : 6 X 4 + 4 = 24 + 4 = 28, 4 X 4 = 16
Answer : 64 X 44 = 2816
Try for yourself the following items using shortcut :
1) 35 X 75
2) 43 X 47
3) 86 X 26
4) 52 X 58
5) 39 X 79
Answers :
1) 2625 2) 2021 3) 2236 4) 3016 5) 3081
SOURCE :
21ST CENTURY MATHEMATICS 6
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Comments
Hi Moondaisy. It is nice to hear from you again. Regards.
44*12
Look at the left side of the equation and think 4 x 1 is 4.
Keep this number in your head.
Next add up the digit 1 and 2 and think, 3 x 4 is 12. Combine the numbers 4 with the 1 in 12. Think 52, this is the partial answer.
End with 4 x 2 is 8. Place the 8 at the end of 52, for the answer 528
With practice you will be able to do this in seconds.
Of course for multiplying by 12 you could always just write down the first digit. (4) Double the same digit and add the rightmost number. 8+4=12. Carry the one to the first number for 52, and double and place the last digit (8). 528.
Or, you could double the entire number (44) to 88. Carry the 8 to 44 for 52, and place the 8. 528.
I solved every problem, it works GREAT! thanks a lot for your work.
Moon Daisy says:
5 months ago
Wow, that's great! I've never come across those before and would love to find out why they work. Maybe if I have time I'll try to work it out! :o)
Thanks, the shortcuts may come in handy with any future maths teaching that I do.