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Number System - Classification -2
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This video is second in the series of videos on number system. It contains classification on Natural number and an important concept based on that.

Vishal Sharma
I am an engineer by education and teacher by choice.I have been training students for CAT exams for 16 years.I have worked with top brands l

Unacademy user
Sir can u provide some videos on descriptive papers........
1. Faculty : Vishal Sharma More than 16 years of experience in CAT training Trained 10000+ students till date

2. Topic for Session NUMBER SYSTEM CONCEPT QUESTIONS BASED ON THEM

3. Natural Number - Classificatiorn Prime Natural Number Co-Prime Composite Perfect

4. Prime Numbers Numbers which are divisible by 1 and itself or Which has only two factors 1 is not a prime number 2 is the only even prime number 3,5,7 the only triplet All prime no are odd . All prime no greater than or equal to 5 are of the 6k+1 or 6k-1 Numbers from 1-50 15 From 51-100 10

5. Let's look at some other types . Composite: Numbers which have more than 2 factors. Perfect Numbers whose sum of proper factors is equal to one. . Co-Prime : Factors which has only 1 as HCF Eg 5,6 8,11 1,30

6. Let's take some more concept on Number:s How many total digits How many total digits do l use If I write from 1-1000 From 0-9,9*1-9 10 - 99,90* 2 180 100 999, 900*3 2700 1000- 4 digits do I use If I write from 1-100 From 0-9 9 single digit numbers From 10-99 90 two digit no 90*2 3 digits for 100 9*1 180 Total digits used 2893 Total digits used 192

7. . How this concept can be Let's take up one more 1- 10000 No of digits used used in CAT? Suppose If I write digits sideways starting from 1234567891011. What is the unit digit of this 100 digit number? 1-999 = 2889 1000-9999 9000*4 = 36000 10000 5 digits Let's Look at the explanation Total 38894

8. Explanation.... .Say from 1-9 9 *1-9 91 more digits.. From 10 to 54 there will be 45 numbers So 45*2 90 Next when we use 5 of next number 55 our 100 digit number is ready...So ans is '5

9. Thank You