Thursday, 6 April 2017

Calculation Tricks II- Multiplying Two Complementary Numbers

Time to get a couple of smart calculation tricks up your sleeve that help you save time!

Complementary Numbers



Calculation Tricks come in very handy in all competitive exams. Not only are they a whole lot simpler but also save some valuable time in IBPS, SSC and other Banking Exams. Read on to find how to multiply a pair of complementary numbers.
So here is the 10th blog in the series of blog posts about smart methods that will help you solve questions in 5- 10 seconds that would otherwise take 30- 45 seconds.
Complementary Numbers

What are Complementary Numbers?

Let’s start by discussing- What are complementary numbers? Complementary numbers are actually a pair of numbers where the number is obtained by subtracting a number from its base. Use of some simple calculation tricks can make it really easy to multiply such numbers. For example, the complement of 7 in numbers to base 10 is 3. Two numbers can be subtracted by adding one number to the complement of the other. Two numbers can also be divided by using successive subtraction.

Example of Multiplying Complementary Numbers

43 x 47 = ?
1) 2021      2) 2521      3)1621      4) 2421      5) None of these

Conventional Method to Multiply Complementary Numbers

The regular method to solve this question is by using pen and paper followed by multiplying 7 with 3, carrying forward 2 and continuing till you finally reach the answer! Trust me that’s a lot of work for a simple calculation that is sometimes just a part of the question and not even a question in itself and spend 15 seconds only to solve it!

Step 1:   
Find the square root
It may look like just 1 step, but involves a whole lot of calculations!


Smart Method to Multiply Complementary Numbers

What if we discuss a really quick and less tedious way of calculating the same by using some calculation tricks!
We can observe that 43 and 47 are complementary numbers because 7+ 3= 10 and 4 is the common base. Such numbers can be easily multiplied in just two steps without tons of calculation.

Step one is multiplying the numbers in the units place
Step 1:
7 x 3= 21

Step two is multiplying the number in the tens place with the next integer
Step 2:
4 x 5= 20

Then to get the answer first write the number combination obtained by multiplying the tens number with the next integer followed by the product of the two complementary numbers.
Step 3:
43 x 47= 2021

No difficult calculations and the correct answer in just 5 seconds! 


Complementary Numbers


Watch this smart method explained by our expert faculty.



Try multiplying these complementary numbers by using the calculation trick!

Question 1: 24 x 26 = ?
1) 724     2) 684     3) 624     4) 1024     5) None of these

Question 2: 77 x 73 = ?
1) 3721     2) 5241     3) 5681     4) 5621     5) None of these


Keep watching this space for more smart methods to master more calculation tricks and keep practicing using these smart methods.


Complementary Numbers


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