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Number System - Rules and Examples

Published on Friday, May 06, 2016
Rules on Counting Numbers


Note:

In the first n counting numbers, there are n/2 odd and n/2 even numbers provided n, the number of numbers, is even. If n, the number of numbers, is odd, then there are 1/2(n + 1) odd numbers and 1/ 2 (n – 1) even numbers.

For example:  from 1 to 50, there are 50/2= 25 odd numbers and 50/2 = 25 even numbers. And from 1 to 51, there are (51+1 )/2 = 26 odd numbers and(51-1 )/2= 25 even numbers.

 The difference between the squares of two consecutive numbers is always an odd numbers.
number system 5

 The difference between the square of two consecutive numbers is the sum of the two consecutive numbers.

Solved examples:

Ques 1. What is the total of all the even numbers from 1 to 400?
number system 3

Ques 2. What is the total of all the odd numbers from 1 to 180?
number system 2

Ques 3. Find the sum of all the odd numbers from 20 to 101.
number system

POWER AND INDEX

If a number ‘p’ is multiplied by itself n times, the product is called nth power of ‘p’ and is written as pn. In pn, p is called the base and n is called the index of the power.

Solved examples:

Ques 4. What is the number in the unit place in (729)59?
Solution: When 729 is multiplied twice, the number in the unit place is 1. In other words, if 729 is multiplied an even number of times, the number in the unit place will be 1. Thus, the number in the unit place in (729)58 is 1.
            So, (729)59 = (728)58 X (729) = (…….1) X(729) = 9 in the unit place.

Note: When you solve this type of questions (for odd numbers) try to get the last digit 1, as has been done in the above example.

Ques 5. Find the number in the unit place in (98)40 , (98)42 , (98)43.
Solution:       (98)4 = (……….6)
            So,       (98)4n =(…………6)

Thus,   (98)40 = (98)4x10 = (…..6) = 6 in the unit place.
            (98)42 = (98)4x10 X (98)2 = (…..6)X(…….4) = 4 in the unit place.
            (98)43 = (98)4x10 X(98)3 = (…..6)X(…….2) = 2 in the unit place.


Note: When there is an even number in the unit place of base, try to get 6 in the unit place, as has been done in the example.

Rule no. 1.

For Odd Numbers

When there is an odd digit in the unit place (except 5), multiply the number by itself until you get 1 in the unit place.
          
  (…………1) n = (……………1)
   (……….3)4n   = (………..1)
   (……...7)4n     =  (………..1)
            
Where n = 1, 2, 3,……….  

Rule no.2

When there is an even digit in the unit place of the given number, then after any times of its multiplication, it will have the same digit in the unit place i.e.
            (…………1) n = (……………1)
            
               (……….5)n = (………..5)

                 (……...6)n =(………..6)


Ques 6. What is the numbers in the unit place when 781, 325, 497 and 243 are multiplied together?
Solution: Multiply all the numbers in the unit place
 i.e., 1 X 5 X 7 X 3; the result is a number in which 5 is in the unit place.
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Ramandeep Singh

Ramandeep Singh - Educator

I'm Ramandeep Singh, your guide to banking and insurance exams. With 14 years of experience and over 5000 successful selections, I understand the path to success firsthand, having transitioned from Dena Bank and SBI. I'm passionate about helping you achieve your banking and insurance dreams.

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