Permutations and Combinations 12 (Sum of digits as integral solution concept) | CAT 2024

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  • Permutations and Combinations by Ravi Prakash | Quantitative Aptitude for CAT 2024
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ความคิดเห็น • 76

  • @worldentertainer5263
    @worldentertainer5263 5 ปีที่แล้ว +57

    In question “ how many nos upto 1lakh will give sum of digits as 13 it should be 17c4 - 7c4*5

    • @ShivamSharma-ig9vp
      @ShivamSharma-ig9vp 5 ปีที่แล้ว +9

      you are pro man:)

    • @bankingsaga8020
      @bankingsaga8020 4 ปีที่แล้ว +1

      Yesss , mine too

    • @parulpatel1497
      @parulpatel1497 4 ปีที่แล้ว +9

      yes, it should be C(7,4) but anyway C(7,4)=C(7,3)

    • @adithya8
      @adithya8 4 ปีที่แล้ว +9

      Its the same thing. He literally said it doesn't matter if its 7C4 or 7C3, because it yields the same value

    • @shivamvarshney7783
      @shivamvarshney7783 4 ปีที่แล้ว +4

      both are equal u can take 7c4 also

  • @abhinandandas2823
    @abhinandandas2823 2 ปีที่แล้ว +39

    18:00 min of this video sir please check 7C4 it should be that you are subtracting

    • @tonymartial1211
      @tonymartial1211 2 ปีที่แล้ว +15

      7c3 and 7c4 are essentially the same

  • @Dinesh__Jandagudem_29
    @Dinesh__Jandagudem_29 ปีที่แล้ว +3

    A+B+C+D=14 and if A=10 or B,C,D any two digit no it becomes 5 digit no greater than 10000 then exclude them

  • @mayankmishr4226
    @mayankmishr4226 2 ปีที่แล้ว +2

    Really great videos sir, love your way of thinking and the way you open my mind! Thank you

  • @AkashGupta-no5ju
    @AkashGupta-no5ju 10 หลายเดือนก่อน +3

    Sir, at 18:00 the answer is wrong i hope so waha par 7C4 hoga.

    • @aiwinct4932
      @aiwinct4932 5 หลายเดือนก่อน

      So what it doesnt matter the value is the same💀😭

    • @aiwinct4932
      @aiwinct4932 5 หลายเดือนก่อน +1

      Ncr=Ncn-r

  • @muskansharma2058
    @muskansharma2058 4 ปีที่แล้ว +3

    Thank you sir!!

  • @tejaljadhav1275
    @tejaljadhav1275 5 หลายเดือนก่อน

    in last question, can we solve by -
    total cases of upto 5 digit - total cases of upto 4 digits = cases of only 5 digits.
    im getting same answer as yours sirs.

  • @nishantsingh878
    @nishantsingh878 4 หลายเดือนก่อน

    what if ths sum is a big number, say 20-100 range. then what number should be alott small a

  • @animeshbiswal8121
    @animeshbiswal8121 4 ปีที่แล้ว +1

    sir in the first question A+B+C+D if sum of digits is 8 then how 1+2+6+0 case be taken it gives sum of digits as 9?

    • @battusajeev
      @battusajeev 4 ปีที่แล้ว +2

      that was just a small mistake

    • @aditisrivastavaas3177
      @aditisrivastavaas3177 4 ปีที่แล้ว

      In ques where 1lakh will give sum of 13 ? 7c3 kyu h ?? It should be 7c4 na kyuki 4 plus sign h sir only told us about this nd here he has written 7c3 whyy??

    • @aditisrivastavaas3177
      @aditisrivastavaas3177 4 ปีที่แล้ว

      PLzz reply anyone who knows it

    • @arpitachaurasia1455
      @arpitachaurasia1455 4 ปีที่แล้ว +1

      @@aditisrivastavaas3177 7c4=7c3 so anyone of it can be written

    • @aditisrivastavaas3177
      @aditisrivastavaas3177 4 ปีที่แล้ว +1

      Thank you @arpita

  • @cumulusmusic100
    @cumulusmusic100 ปีที่แล้ว

    Thank you Sir 🙏.

  • @Super-lj1rf
    @Super-lj1rf ปีที่แล้ว

    Thanks

  • @rupalichaudhary7128
    @rupalichaudhary7128 4 ปีที่แล้ว +3

    Taking digits as 14.....us ques mn A>=10 kyu h? It should be A>10 or A>=9 right? Please replyy

    • @akshat9282
      @akshat9282 4 ปีที่แล้ว

      a>=10 is there because you can't count 10,11,12...and so on. these numbers are subtracted. so it should be a>=10 or a>9. don't worry, I think you are confusing meaning of inequality signs a little bit. try to understand them on TH-cam. it'll make things clear✌️

  • @AshishSingh-gz4lw
    @AshishSingh-gz4lw 3 หลายเดือนก่อน

    Sir, in the first question why have you taken till 4 digits only?

    • @Kapilsharmaashow
      @Kapilsharmaashow 3 หลายเดือนก่อน

      Because you have to find numbers upto 10000 which means 1 to 10000 bus 10000 sum is (1+0+0+0+0= 1) therefore we don't have to include 10000 except that we have 1 to 9999 in which we have 1,2,3 and 4 digit number only

  • @dhairyamankad5516
    @dhairyamankad5516 2 ปีที่แล้ว

    Thank you so much :)

  • @tonymartial1211
    @tonymartial1211 2 ปีที่แล้ว

    thank u sir

  • @kshitijbalonie4361
    @kshitijbalonie4361 4 ปีที่แล้ว +1

    Thank you sir

  • @aryaratna_bhattacharya
    @aryaratna_bhattacharya 2 ปีที่แล้ว +1

    Why can't 13C4 Numbers (5 Digit Numbers) give a sum of 9? As, 9

    • @nareshramesh3519
      @nareshramesh3519 2 ปีที่แล้ว +1

      bcos 5th digit cant be zero ,if it becomes 0 then it will be 4 digit number example ( 05430 = 5430 ). I hope i cleared your doubt

    • @apoorvsingh9507
      @apoorvsingh9507 ปีที่แล้ว

      @@nareshramesh3519 then do (13c4-12c3) in which 13c4 includes all cases up to 5 digits and 12c3 will include all cases up to 4digits their difference will give you your answer.

  • @mindfullmallu7511
    @mindfullmallu7511 3 ปีที่แล้ว

    Lovn' p&c

  • @irfansheikh8
    @irfansheikh8 3 ปีที่แล้ว +27

    I attended the classes of Bansal sir in 11&12 th class but believe me sir you are a gem👍

  • @janvib27
    @janvib27 8 หลายเดือนก่อน +6

    Feels like Magic tricks being revealed! Permutation and combination never felt so easy! Thank You Sir!

  • @traders_chart_Lab
    @traders_chart_Lab 5 หลายเดือนก่อน +2

    At 10:00 how can A get 10 ? Bcoz that will be 2 digit na if a = 10 , then abcd will be 5 digit no , that is violates qus

    • @prateekbirthal9649
      @prateekbirthal9649 3 หลายเดือนก่อน +1

      That's the point, we are removing all the invalid cases.

    • @abhinavpratapsingh8431
      @abhinavpratapsingh8431 19 วันที่ผ่านมา

      10, value is 10 , its not that we are putting A as 10 as a digit beside BCD

  • @prajwalr9134
    @prajwalr9134 5 ปีที่แล้ว +16

    Keep up the good work. The classes are too good and I Love the sequence how the classes go. A small bit of info- your website is down which would reduce your traffic so please take care. Thanks and cheers!

    • @Rodha
      @Rodha  5 ปีที่แล้ว

      Thanks

  • @somalakshmishivani4773
    @somalakshmishivani4773 3 ปีที่แล้ว +2

    A+B+D+C=13. abcd are digits0to9. Then10,11,12,13, are not under0 to9 we should A+B+C+D=4. 7C3 is answer ...........please explain me....not explained my doubt well please understand

  • @MithunGaming
    @MithunGaming 12 ชั่วโมงที่ผ่านมา

    for the sum of digit is 14 case, in one case if we say A >= 10, wouldnt it give all the cases where B will be greater than 10, etc? since this will give us cases in which every shuffling is possible, like sir said in the last sum? so we should not multiply 4 * C(7,3), but just C(17,3) - C(7,3)

  • @SrushtiMenpara
    @SrushtiMenpara หลายเดือนก่อน

    In the sum of digits 14 question what if..
    A>10 and B>10 also don't we have to count for those cases as well?
    and if there's one case where A>10 AND B>10 as well ...according to this method this case will be treated as 2 different cases which is actually a similar case. we removed it twice.
    Help, please.

  • @chinmaysomani5387
    @chinmaysomani5387 4 ปีที่แล้ว +4

    best channel ever

    • @ankitsinha5382
      @ankitsinha5382 4 ปีที่แล้ว

      Sir teaches live on Unacademy plus. You can directly contact him there. His full content is not here.

  • @dikshajatwani2764
    @dikshajatwani2764 5 ปีที่แล้ว +1

    sir,how can we distribute distinct digits using this method as we distribute only similar things using this method?

    • @atharvachoudhary6974
      @atharvachoudhary6974 3 ปีที่แล้ว

      Think about each digit x as being x number of chocolates.

  • @the3ambreeze
    @the3ambreeze ปีที่แล้ว

    Number of 7 digit numbers the sum of whose digits is 61 is?
    I am unable to solve as the answer is coming in negative. What am i doing wrong?

  • @amrishpatidar2579
    @amrishpatidar2579 5 ปีที่แล้ว +1

    awesome lecture

  • @dhruv5774
    @dhruv5774 ปีที่แล้ว

    i didnt understand the first question

  • @siddharthchhibber160
    @siddharthchhibber160 3 ปีที่แล้ว

    How many 5 digit numbers will give digital sum as 26

  • @tejpratapsingh5480
    @tejpratapsingh5480 ปีที่แล้ว

    tq
    ;

  • @piyushmundra7511
    @piyushmundra7511 11 หลายเดือนก่อน

    What will be the answer if the last 2nd question is changed to 22, i.e. How many nos upto 1L will give sum of digits as 22.

    • @piyushmundra7511
      @piyushmundra7511 11 หลายเดือนก่อน +1

      Answer
      Total cases - 26C4 (14950)
      Less:
      Cases where either of the 5 digits is more than or equal to 10 = 16C4*5 (9100)
      Add: (duplication case)
      Cases where 2 digits out of 5 digits is more than or equal to 10 = 6C4*5C2 (150)
      Ans: 14950-9100+150 = 6000

  • @pranaykolte6817
    @pranaykolte6817 4 ปีที่แล้ว

    Can we get quizz of this lecture?

  • @amanbansal7932
    @amanbansal7932 5 ปีที่แล้ว

    Do you teach in Time Bangalore?

    • @periyasamyn4857
      @periyasamyn4857 5 ปีที่แล้ว +1

      He is teaching at IMS, Koramangala... Eve 6 to 8 weekday batch!!

    • @BharatSingh-mi9xo
      @BharatSingh-mi9xo 4 ปีที่แล้ว +6

      @@periyasamyn4857 Koramangala guys are so lucky.

  • @ankurhooda4326
    @ankurhooda4326 3 ปีที่แล้ว +1

    in the first question, total numbers are asked so wont it be (11C3 - 1) as 0 is not considered while counting?

    • @ankurhooda4326
      @ankurhooda4326 3 ปีที่แล้ว

      and same will go for every question you solved, as in last question the specification is provided by you only that 0 will be not considered while numbering.

    • @harshitabhansali3638
      @harshitabhansali3638 3 ปีที่แล้ว +5

      Take these questions as chocolate and its distribution like
      8 chocolates should be distributed among 4 friends in such a way that 0 value can be allowed so if we give 0 choclate to 3 friends then remaining one directly comes comes out as 8 "(0,0,0,0) can't be possible" like A+B+C+D = 8 for whole number solution N+R-1 C R-1 , 8+4-1 C 4-1 = 11C3

    • @ankurhooda4326
      @ankurhooda4326 3 ปีที่แล้ว

      @@harshitabhansali3638 Yes got it! Thanks )

  • @annkkzzgamer7999
    @annkkzzgamer7999 ปีที่แล้ว

    Sir first question can be done by using AP... An AP with common difference of 9 have same digital sum... As I started it with 8,17,26........9998. There are 1,111 number... Anyone please tell me where am I wrong?

    • @princewable6854
      @princewable6854 ปีที่แล้ว +2

      The 1st que is asking about sum of digits not the digital sum so your method is incorrect.

  • @dhruvsharma9083
    @dhruvsharma9083 3 ปีที่แล้ว +1

    *Can someone tell me if i just dumbly done the same thing long way, or is ir another way of thinkng?*
    I tried to solve it with my approach. Finally reached on it but too complex and maybe mine is same and just doing the long way.
    Its like : number number can be above 9 so conisder each a case where ever number is 10,11,12,13,14 (or a to say reversly a case where sum of other 3 digits is such that, it causing the 4 th number to go beyond 9).
    It was like ,
    For every digit 14 turn by turn , (4 ways)+
    Every digit 13 , (4 * 3c2)+
    Every digit 12, (4*4c2)+
    Every dig 11, (4* 5c2)+
    Every dig 10, (4* 6c2) =k
    So 17c3- k =0 .
    *Can someone tell me if i just dumbly done the same thing long way, or is ir another way of thinkng?*

    • @Rodha
      @Rodha  3 ปีที่แล้ว +8

      When u learn a good concept, note it. Always utilise the brain in how to make a longer method shorter, never do vice versa :)

    • @dhruvsharma9083
      @dhruvsharma9083 3 ปีที่แล้ว

      Sure . Thanks !

    • @mayankmishr4226
      @mayankmishr4226 2 ปีที่แล้ว

      @@Rodha Epic reply sir, still cudos to dhruv, thats a different way to think for sure