How to Multiply Numbers close to 10, 100, 1000, 10000s In Your Mind

 

Just like in the last video we learnt how to construct tables for numbers like 19 and 39, in this video we move a step further and learn the same for numbers like 31 and 27. This is a fairly easy method to calculate tables for bigger numbers without having to learn them. So let’s begin. For constructing the table of 31 we need to first find the rounded off number nearest to its 10. 30 is the nearest rounded off number to 31. 31 can also be written as 30 + 1. We earlier discussed that 30, 20, 40 are nothing but 3 x 10, 2 x 10 and so on. Thus, 30 + 1 can also be alternately understood as adding 3 to the digit in the tens place and then adding 1 to the digit in the units place.

Note that in the previous video we had subtracted 1 because 19 is 20 – 1. Here 31 is 30 + 1, hence 1 is being added. So 31 x 1 = 31

For 31 x 2, add 3 to the tens place (3 + 3 = 6) and add 1 to the units place (1 + 1 = 2) making it 62.
Therefore, 31 x 2 = 62.

For 31 x 3, again 3 to the tens place (6 + 3 = 9) and add 1 to the units place (2 + 1 = 3) making it 93.
Therefore, 31 x 3 = 93, and so on.

Note that the pattern of numbers being formed has a thing in common. The number in the tens places are forming the table of 3 and the numbers in the units places are forming the table of 1. When the table of 1 reaches 9 in the next step it gives a carry of 1 thus adding 1 to 30 making 31 x 10 = 310.

Let us now see the table for 27. A slightly different approach is followed for this number. Instead of rounding it off to the nearest 10 we round it off to the nearest 5 number. 25 is nearest to 27. Hence we will visualise 27 as the addition of the tables of the numbers 25 and 2 (since 27 = 25 + 2).

Having written the table for both we can now add them to get the table for 27. Like

27 x 1 = 25 + 2
27 x 2 = 50 + 4
27 x 3 = 75 + 6 and so on.

So in this video series we have three ways to construct tables for numbers. For numbers like 39 and 49 round them up to 40 and 50. For numbers like 31, 32 or 51, 52 round them up to 30 and 50. While for numbers like 23, 24 or 26, 27 round them up to 25.

By using these methods you can easily find the tables for any number.

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