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Thursday, February 26, 2004 - 03:57 PM
Got 5 minutes to spare? That's all the time you need to learn how to quickly multiply two numbers from 11 to 19 in your head. With this trick, you will be able to multiply any two numbers from 11 to 19 in your head quickly, without the use of a calculator.
I will assume that you know your multiplication table reasonably well up to 10x10.
Lets try 15 x 13.
1. Always place the larger number of the two on top in your mind.
2. Then draw the shape of Africa mentally so it covers the 15 and the 3 from the 13 below. Those covered numbers are all you need.
3. Now add 15 + 3 = 18
4. Add a zero behind it (i.e., multiply by 10) to get 180.
5. Multiply the covered lower 3 by the single digit above it, in this case the "5" (3 x 5 = 15)
6. Add the products from steps 5 and 6 to get your answer. 180 + 15 = 195.
That's it! Wasn't that easy? Practice it on paper first!
I will assume that you know your multiplication table reasonably well up to 10x10.
Lets try 15 x 13.
1. Always place the larger number of the two on top in your mind.
2. Then draw the shape of Africa mentally so it covers the 15 and the 3 from the 13 below. Those covered numbers are all you need.
3. Now add 15 + 3 = 18
4. Add a zero behind it (i.e., multiply by 10) to get 180.
5. Multiply the covered lower 3 by the single digit above it, in this case the "5" (3 x 5 = 15)
6. Add the products from steps 5 and 6 to get your answer. 180 + 15 = 195.
That's it! Wasn't that easy? Practice it on paper first!
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Comments
very useful. i learned this some time back and i've come to call it the "mango method" because of the shape that you draw around the digits. it has helped me a lot during contests.
e.g..24x24..
24+4=28
28x20(multiply by 20 instead of 10)=560
4x4=16
560+16=576
e.g..24x24..
24+4=28
28x20(multiply by 20 instead of 10)=560
4x4=16
560+16=576
Thank you!
2.Adding 43+4 = 47
3. multiplying the multiple of 10 of tht base which u had left behind i.e in this case 30
i.e
47x30 = 1410
4.multiplying the last two digits and adding it to result obtained in 3
4x3 =12
1410+12 =1422
5.Finally
Add multiple of 10 of higher num to the result in 4 i.e
1422+40=1462
Please verify this if correct, by taking test cases b/w 99x99 like 98x44 etc.
Wow!! that trick really eases the calculation as well as giving it a tinge of fun.
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