Aptitude - Permutation and Combination - Discussion
Discussion Forum : Permutation and Combination - General Questions (Q.No. 14)
14.
In how many ways can 21 books on English and 19 books on Hindi be placed in a row on a shelf so that two books on Hindi may not be together?
Answer: Option
Explanation:
In order that two books on Hindi are never together, we must place all these books as under:
X E X E X E X .... X E X
where E - denotes the position of an English book and X that of a Hindi book.
Since there are 21 books on English, the number of places marked X are therefore, 22. Now, 19 places out of 22 can be chosen in
| 22C19 = 22C3 = | 22 x 21 x 20 | = 1540 ways. |
| 3 x 2 x 1 |
Hence, the required number of ways = 1540.
Discussion:
27 comments Page 1 of 3.
Mahanthesh naik said:
9 years ago
Correct ans is= 22c19 * 21! *19!.
Jyothi said:
10 years ago
ncr = nc(n-r) so 22c19 = 22c(22-19) which is 22c3.
Mansi said:
1 decade ago
Why are we not calculating the ways to arrange English books by doing 19?
Sreeejith said:
1 decade ago
Hey guys I have hit the wall with the same question Is it permutation or combination?
Somia said:
1 decade ago
The total no.of arrangements that can be made by the word rainbow are:
7! = 5040 words.
Let us consider, the "row" as a single letter so now the remaining letters are "ainb" four letters, then it is total a 5 letter word,
The no. of ways for the five letter words are ways, 5! ways = 120 words. And it remains same for bow.
Am I correct please correct me if I am wrong?
7! = 5040 words.
Let us consider, the "row" as a single letter so now the remaining letters are "ainb" four letters, then it is total a 5 letter word,
The no. of ways for the five letter words are ways, 5! ways = 120 words. And it remains same for bow.
Am I correct please correct me if I am wrong?
NISHA said:
1 decade ago
Find the number of words that can be formed by using all the letters of the word RAINBOW.
How many of them end ROW and BOW?
How many of them end ROW and BOW?
Preeti said:
1 decade ago
Yes, the question is about arrangement and the solution given is the combination of Hindi books, the selection is done in 22C19 ways but what about arranging them?
Himaja said:
1 decade ago
21c19 is the way of choosing the places for 19 hindi books, but what about arranging them?, according to me I thought that 21c19 is the way to choose places and 19p19 for arranging them. Can anyone say is this right or wrong, please.
Saurav said:
1 decade ago
The solution for this question will be 22C19. Because it is question related to combination because all the book of english are identicals. No need to take 21!.
Saurabh said:
1 decade ago
So I think 23c19 is the better choice. And I think the arrangement of the english or hindi books within themselves doesn't matter according to question. Please reply for the choice between 22c19 or 23c19.
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