Learn Tables only till 5x5. Rest can be derived from that...

Lets get back to our school days of 1st standard where we were forced to learn tables upto some where around 15... And now a days even worse, children learn tables upto some 23... My question is "Is it all really required??". No, not really.., you need to know tables only till 5x5, the rest can be derived very easily and with out even piece of paper and pencil. You can recite tables at the same speed as you recite it after memorizing. And for sure no body is going to know how you are reciting it... Here ill explain a very simple technique to derive  the multiples of larger numbers ranging from 6.., teach this method to children and make them practice it for a few days and you can see them directly reciting tables of 43 without even learning the tables of 6... With this you can reduce their burden and yeah even yours to a very large extent ;-)

So here we go assuming you know the tables upto 5x5. Now assuming this suppose we wanna find the value of 8x7..., how do we do that...?? Write down a small chart as show below..,

Here we have two numbers 8 and 7 whose product is to be found.

• Initially write down those numbers one below the other as shown in the first column of the chart.
• Now consider the first number 8. It is 2 less than the base 10 i.e 10-2=8. So writ down -2 on its left.
• Next consider number 7 which is less than 10 by 3. So write down -3 next to 7.
• Now multiply the numbers 2x3=6 and write it down below as shown in the second column of chart which form one part of answer. 
• Now do cross subtraction of either 8-3=5 or 7-2=5. So the number 5 form the other part of the result. 
• Combine both to get the final result 56.

Frankly speaking you need to practice with the chart only initially for two or three days. Again it deppends on you. If you are good enough no need to practice at all. You can do all the work mentally and the result is there within no time... 

Now consider another example of 13*6. The chart is again shown below...,

•  Write down 13 and 6 one below other as in first column of chart.
• 13 is 3 more than 10. so write +3 next to 13
• 6 is 4 less than 10. so write -4 next to 6.
• multiply (+3)x(-4) = -12 and write down as shown in the chart. Here -1 is a carry and -2 is written down below.
• now since negative value cannot be there in result, we borrow 10 from left and write the result 10-2=8. which forms one part of answer.
• Since we borrowed 10 from left we now have on the left -1-1=-2.
• Now cross add 6+3 or 13-4 to get 9. and writ down as below.
• Now we have 9-2=7. which forms other part of answer. 
• So final result is 78....,

This example says what to be done for the numbers above the base and also what to do if there is a carry. The carry must be added to the left or effectively speaking here we have borrowed one because of the negative sign. If it was a positive sign we just simply need to add it to the left part of the answer. Hope this method will help those who find difficulty dealing with the tables... :-) Thank you..., 

Squaring two numbers ending with 5 (Suitable for only small numbers)

In this post i will tell u how to multiply two numbers ending with 5 like 25, 35, 45 and so on... Can u image how simple it is to square such numbers??? Well if you cant then stop because before you can imagine that you can find the result itself :-)... So let me explain you this simple method...

Consider finding the square of number 35. This number end with 5 rite?? Well then for the same reason we can say that its square ends with 25!!! How?? Consider the square of any number like 5, 15, 25 etc... the squares are 25, 225, 625 etc... So amazing to see that the squares end with 25. Isn't it??So here in our example of 35*35 also the result end with 25... Now we must find the remaining part of the result. For this consider the remaining digits except 5 in the number considered.. Here in number 35 the digits except 5 is "3". So the number next to digit 3 in number system in "4". Hence find the product of 3*4=12 which will be the remaining part of the result... So final result is "1225". Similarly you can apply this technique for even numbers like 105.

For 105, as explained the final result must end with 25. We have "10" as remaining digits if we exclude the digit 5 in 105. the number next to 10 is "11". So product 10*11==110. So final result is 11025... Hope this method will be very useful to you all... Thank you...

Simple method to Square numbers near to the base

As children we have always had a difficulty dealing with the 9 tables. Atleast for me it was a real time task to multiply large numbers involving 9s like 998*998 etc... But I had this difficulty till I realised the importance of number nine and the ease with which it can be dealt with. Speaking truly numbers involving 9 are the easiest to multiply. But not by the methods we have studied in our school curriculum.

Before I tell you how to multiply numbers involving 9 let me just brief you about the importance of number 9. Every number has its own importance. Number 9 is of special significance among all the basic numbers i.e. 1,2...9. The question of why is it so sinificant can be answered with some few simple properties of 9.

1. Sum of the digits in a number(called basic number) divisible by 9 always turns to be 9. for example 27 = 2 + 7 = 9, 4437 = 4 + 4 + 3 + 7 = 18 = 1 + 8 = 9. Hence to find the remainder of a number after dividing by 9 just add the digits in that number and reduce it to a basic number which will be the remainder. For example the remainder of 5467 after dividing by 9 is 5 + 4 + 6 + 7 = 32 = 3 + 2 = 5(remainder).
2. To find the result of addition of 9 to any number just subtract 1 from the numbers unit place and add 1 to its tens place. for example 2343 + 9 = 2352. How to do this?? Consider the number 2343. To add 9 to this just subtract one from its units place i.e 3 - 1 = 2 and add one to its tens place i.e 4 + 1 = 5. Hence the result is now 2352.
   

There several such properties of number 9. I will try to get you a list of them in my future posts...

Now we know how simple it is to deal with number nine for finding the remainder and for adding it to other number... But these tasks can be done with no difficulty in traditional methods also... But what about multiplying numbers like 999 * 999 or 999998 * 999998 etc... Can you give the answer without a piece of paper and a pencil??? Yes you can... Follow the method I explain below...

Let me take an example to explain this. Consider finding answer for 98 * 98...

• Here number 98 is close to base 100 with a difference of 2. i.e 100 - 2 = 98.
• Since 98 is 2 less than 100 just subtract it from 98. we get 96... Keep this 96 which forms one part of the answer.
• Now since we subtracted 2, find the square of 2 i.e 2*2=4. And since we have choosen the base to be 100 initially we have to pefix 0 to number 4 i.e 04. This forms the other part of the answer.
  
• Now combine the result of above two steps to get the final result as 9604 :-)

This is the simplest method to square a number which is near to the base like 99, 98, 9999999999999996 etc... Take any large number near to the base and this method works even if your calculator dint work :-)

For example consider another number 999996 * 999996. So this is near to 1000000 and is less by 4. So result is 999992000016...

And this method also works for the numbers like 10004, 1008 etc. which are above the base but with a slight modification. For example to find the square of 1008 which is near to 1000 and more than 1000 by 8 we do as follows... Add the number 8 to 1008 to get 1016 and also find the square of the number 8 to be 64 and append it to 1016 to get 10160064.

Now if you are wondering how this method yiels a correct result for any number then here is a simple mathematical proof...

We all know a simple algebraic identity which we have used merely to solve the equalities in our high schools but never realised that it can be used in real life. i.e the simplest and our favourite a*a - b*b = (a+b)(a-b). The method i explained above is derived from this identity. As we know now our aim is to find square of a number say a*a. so we now have...
a*a = b*b + (a+b)(a-b)
say here a=98, our first example. We can choose a random number b. I will choose b=2 because its eases my multiplication task as the term a+b will now be 98+2=100. Now just substitute for a=98 ans b=2 in above identity...
98*98 = 2*2 + (98+2)(98-2)
= 4 + 100*96
= 4 + 9600
= 9604

Hope this post added some information to your database :-). Ill explain few more methods in subsequent blogs... Thank you...