What does the following multiplications have in common and can be calculated in a matter of a fraction of a second in your own mind and without the aid of an electronic device:
1.) 24 x 26 =
2.) 33 x 37 =
3.) 42 x 48 =
4.) 55 x 55 =
6.) 69 x 61=
The answers are of course:
1.) 624
2.) 1221
3.) 2016
4.) 3025
5.) 4209
But you are probably saying that I used a calculator to do it. The simple answer is no, I did it mentally. If you look at the second digits of all the above individual multiplications, they all add up to 10.
Then in that case all you have to do is to multiply the first digit that is common to both the numbers by the next higher digit and write it down. The next step is to multiply the two second digits of the two numbers that you are calculating and stick it next to the number that have just written down. That is your answer.
So for the first calculation of 24 x 26, the second digits of both the numbers adds up to 10. i.e. 6+4 =10. In that case you can proceed by multiplying the first digit that is common to both i.e number 2 by the next number that is greater than 2 which in this case is 3. i.e. 2 x 3 = 6 and then multiply the second digits 6x4=24. All you have to do is write down 6 and put the 24 next to it. You get the answer 624.
Similarly, for 2.) 3x4=12, and 7x3=21. Write down 12 and add 21 next to it and your answer is 1221.
For 3.) 4x5=20, and 2x8=16, hence your answer is 2016.
For 4.) First digit 5x6=30, and second digits for both is 5. Hence 5x5=25........answer 3025
Finally 5.) 6x7=42 and second digits are 9x1=09. You cannot just write 9 as all the multiplications of the second digits should have two numbers. So, the final answer is 4209.
Just something simple to teach your kids. The kids can the teach some math to their teachers.
1.) 24 x 26 =
2.) 33 x 37 =
3.) 42 x 48 =
4.) 55 x 55 =
6.) 69 x 61=
The answers are of course:
1.) 624
2.) 1221
3.) 2016
4.) 3025
5.) 4209
But you are probably saying that I used a calculator to do it. The simple answer is no, I did it mentally. If you look at the second digits of all the above individual multiplications, they all add up to 10.
Then in that case all you have to do is to multiply the first digit that is common to both the numbers by the next higher digit and write it down. The next step is to multiply the two second digits of the two numbers that you are calculating and stick it next to the number that have just written down. That is your answer.
So for the first calculation of 24 x 26, the second digits of both the numbers adds up to 10. i.e. 6+4 =10. In that case you can proceed by multiplying the first digit that is common to both i.e number 2 by the next number that is greater than 2 which in this case is 3. i.e. 2 x 3 = 6 and then multiply the second digits 6x4=24. All you have to do is write down 6 and put the 24 next to it. You get the answer 624.
Similarly, for 2.) 3x4=12, and 7x3=21. Write down 12 and add 21 next to it and your answer is 1221.
For 3.) 4x5=20, and 2x8=16, hence your answer is 2016.
For 4.) First digit 5x6=30, and second digits for both is 5. Hence 5x5=25........answer 3025
Finally 5.) 6x7=42 and second digits are 9x1=09. You cannot just write 9 as all the multiplications of the second digits should have two numbers. So, the final answer is 4209.
Just something simple to teach your kids. The kids can the teach some math to their teachers.
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