After seeing the heading that I’ve used above, many people will wonder what is I’m going to write about. Some will think that I’m referring to our recent pretty batch queen. NO, I’m going to write about the prettiest of all the queens. She is MATH. Today I’m going to reveal some tips which make her the prettiest. There’s something called multiplication (all of you know that word for sure, as we all are undergraduates) and here are some simple tricks of it. Some of you may already know this. I thought of starting from a multiplication of numbers by 9, the bad one:
As most of us know, the multiples of 9 have the property that, their digits add up to 9.
Example: 9 × 2 = 18
And 1 + 8 = 9.
When multiplying 9 by any single digit (1-digit) number, the first digit of the answer is 1 less than the multiplier.
Example: 9 × 3 = 27 begins with 2.
So that it’s easy to find the next digit of the answer by reducing the first digit of the answer from 9.
And when multiplying 9 by any 2-digit number, then add one to the first digit of the multiplier and minus that from the multiplier. So that you can get the first two digits of the answer and the next digit can be found out by the summation trick of any multiple of 9. (10,20,30,40,50,60,70,80,90 are exceptional cases).
Example: 9 x 13
The first digit of the multiplier is 1. So that adds 1 to it.
Deduct 2 by the multiplier
13-2 = 11
Then the next digit can be found by equaling the summation of all the digits of the answer to 9.
Example: 9 x 89
The first digit of the multiplier is 8,
So , 8+1=9
The first digits of the answer are,
The last digit of the answer is 1 (8+0+1=9)
There are ways of multiplying 9 by 3-digit, 4-digit, 5- digit numbers and so on. But for those, we can use a calculator. Some will think, then why do we need the above tricks to multiply 9 by 1,2, -digit number.. We can use a calculator for that too.
Yes you can. But once you get familiarized with the above methods, these will cost you a lesser time to get an answer, than the time of using a calculator. Secondly this is a trick to square a 2-digit number that ends in 5, Multiply the first digit in the number by the next higher digit, then attach 25 at the end.
Example: Let’s consider, 352
Then the first digit is 3 and the next higher digit is 4.
Therefore, 3 × 4 = 12;
Then attach 25 at the end
The answer is 1225.
To multiply a number between 10 and 20 by a 1-digit number, multiply the 1-digit number by 10, then multiply it by the second digit in the 2-digit number, and add the products.
Example: consider 13 × 6
The number between 10 and 20 is 13 and the 1-digit number is 6.
Therefore, multiply the single digit number by 10 and also multiply the single
digit number by the second digit of the number which is between 10 and 20.
(6 × 10) + (6 × 3)
Add the two products,
60 + 18;
To multiply two numbers that are both between 10 and 20, add the first number and the last digit of the second number, multiply the result by 10, then add that result to the product of the last digits in both numbers of the original problem.
Example: Consider product of 13 and 14
The first number is 13 and the last digit of the second number is 4.
Hence, 13 + 4 = 17,
And multiply the above answer by 10,
17 × 10 = 170,
Add the last digits of the two original numbers,
3 × 4 = 12,
Then add the two answers,
170 + 12 = 182;