After paying huge pile of money for books and fraud coachings, one is left with only disappointment.... But then Ravi sir with his video of Rodha Channel appears and takes away all the tensions of Quant, Lr, Di,etc and leaves us with full knowledge about each concept..... Thank you sir.... I can miss my coaching classes but never dare to forget watching your video even on a single day💝💝
*Two common doubts:* 1. *Reverse is not true* It means all prime numbers will be of the form 6k+-1. But all numbers which are of the form 6k+-1 are not prime numbers. For example, if you take the prime number 13, it is of the form 6k+-1 ie, (6×2)+1 . But if you choose a random value for k, for example k=4, (6×4)+1 = 25 which is not a prime number. So that's what he means by "reverse is not true" 2. *Odd number question* They are all odd numbers. The equation for odd number is 2k-1. So if we take first term and equate, 2k-1=1, solve, k=1. For the last term, 2k-1=91, solve, k=46
Need more teachers like you. This is by far the most useful channel for CAT. I have the study material of TIME and I can say topics are covered in depth in these videos. Thanks a lot, Sir.
Same I was going through my cat books but couldn't understand any examples of those books so I came looking for explanation of these topics and was lucky enough to find this hidden gem.
Sir in question 1+3+5------+ 91? You have taken it in the form of 2k-1 but odd numbers can be in the form of 2k+1 as well. So, can we take k=45 and and square 45. Can you please explain why you have taken it 2k-1 and not 2k+1? Please sir
@@nandinisatdeve13 they are all odd numbers. The equation for odd number is 2k-1. So if we take first term and equate, 2k-1=1, solve, k=1. For the last term, 2k-1=91, solve, k=46
For example (******+++++++) consider it as a numbers You have to find +++++++ ? For this you have no formula to add numbers by middle but we have formulae for adding from starting so Subtracting (******)from(******+++++++) You will get ++++++ thats what we need
Thank you so much sir, it's very helpful for us.. Sir one query why odd form no. is true for 2k -1 and not for 2k +1?. Sir, in your ques also 1+3+5+....+91. Here, we are taking 2k-1= 91 Answer is 46 and if, 2k+1= 91 Answer is 45. So we should not consider 2k +1 sir?
Sir I'm starting of my preparation with number system, should I finish all the lecture videos (of number system) to go quizzes or should I carry them on side by side?
Sir why don't you add ppt slides in a folder for downloads. Kudos to you for your great initiative,you way of teaching and content is just amazing.Where all teachers are busy in unacedmy,you are the one who has provided free quality content.
@@aadishjain7454 No , because in 7/6 Ans is 1 (positive 1) but in 5/6 Ans is -1 (when it is divided by 6 ) or 5 ( when it is not divided by as numerator is smaller so)
As per my understanding, even and odd numbers can be negative, I.e -2, -4, -6 are even numbers and -1,-3, -5 are odd numbers. Could you please share the source which states that even and odd numbers are non-negative?
22:04 you are saying that reverse is not a prime no ................ BUT 6(5)+1 { where k = 5 , which is a reverse of 6 } = 31 , which is a prime no. .................... & 6k-1 -------- puting k=4 [ which is a reverse no. of 6 ] gives us the answer 23 , which is a prime no. ....... please answer me
sir im confused in the first question of odd no. i think the no. of odd numbers will be 45 and not 46, as if we go by the formula 2k-1=91 so 2k=90 and l will be 45. please correct me if i'm wrong.
Similarly, can I also say that all prime numbers except 2 are odd numbers(2k +/- 1) but reverse is not true? Reference :- Prime Number form - (6k +/- 1).
u can take both but if u r taking 2k-1 as general from so 2k-1=91 k=46 and if u r assuming 2k+1 that means k=0 for first term thus, 2k+1=91 k=45 so 45+1=46 are total no.
Sir I love ur teaching but I didn't understand last one which u have explained that 6k+1...in that whn we divide...by 6...that is if 1/6 ....remainder is 4...nd 6k divided by 6 and the remainder is k...nd how did u get the remainder s...1 nd 0 ...and next one even...6k-1...I have stucked wth these 2... really not only me....I have forwarded to my frnd even he didn't get it... could u please explain for us sir😢
For the first term if we put 2k+1, then k will be 0. Therefore, it will not follow the pattern of summation of odd numbers starting from zero(1+3+5....+(2n-1)) and hence we will not be able to find the answer by simply calculating n^2.
Take the example of 1001. When divided by 6, the remainder is - 1.but it is not a prime though it satisfies 6k+1. In short every prime no. can be expressed as 6k+1 or 6k-1 but every no. That can be expressed as 6k+1 or - 1 is not a prime no.
The formula of squares starts from 1 square okay? In the question the series starts from 11square. How will we solve now? So we take 1-20 sq usme se 1-10 sq minus krenge toh 11-20 sq wali series bachegi. Hope it helps.
Hi Saumya. There's a formula : 1sqaure+ 2sq+ 3sq +4sq .......... +N sq = n(n+1)(2n+1)/6 right? Now the qes says find 11sq + 12 sq + 13 sq ....... 20sq? How would you do it? If you say using the same formula mentioned above WOULD BE WRONG because the formula starts from 1 sq not 11 sq. So to solve, you will first take (1sq + 2sq +3sq ....... 20sq) - (1sq + 2sq + 3sq.....10sq) NOW when we open we see ( 1sq + 2sq + 3sq.... 10sq ) will cancel out and you'll be left with (11sq + 12sq + 13sq .... 20sq) and thus you get the answer.
Where are the videos sir is taking about basics remainders and other rules in more than 15 videos , i cant find them if anyone cant drop the link i will be thankful
I have a doubt .plz someone clear it .In the question 2 of summation part . ques is 11^2 but in soln sir solved it taking 10^2.can anyone tell me why ?
Because the formula is applicable for series starting from 1 so he is considering at first 1-20 and from that subtracting the first 10 terms to get the actual answer.
There is a mistake in calculation sir in ques based on submission of square no u have taken 10×21/6 as common if u remove 10 from 20 it remains 10 not 2 u have multiplied 2×21instead of 10×21
Exactly that's what Sir is trying to tell. Reverse is not true. See, it is true that when we divide any prime no by 6 it leaves 1or 5 but it is not true if we take any number and apply in 6k+1 or 6k-1 to be called as a prime no. He mistakenly took 25.
