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 2 of 3.
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?
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!.
Nikhil Tambi said:
2 decades ago
How there are only 19 spaces left for books X, and why we are calculating 22C3 instead of 22C19?
Balakumar said:
2 decades ago
Hi Nikhil,
The value of 'r' in combination can be replaced by (n-r), we can use the value which ever is simpler to calculate.
Thank You.
The value of 'r' in combination can be replaced by (n-r), we can use the value which ever is simpler to calculate.
Thank You.
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?
Sreeejith said:
1 decade ago
Hey guys I have hit the wall with the same question Is it permutation or combination?
Mansi said:
1 decade ago
Why are we not calculating the ways to arrange English books by doing 19?
Phanindra said:
2 decades ago
Why he begin arrangment with hindi book? and how he got the 22 places?
Yog said:
2 decades ago
What is the difference between permutation and combination?
Jyothi said:
10 years ago
ncr = nc(n-r) so 22c19 = 22c(22-19) which is 22c3.
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