Discussion
Home ‣ Aptitude ‣ Permutation and Combination Comments
- Question
- In how many ways can the letters of the word 'Director' be arranged so that the three vowels are never together?
Options- A. 1800
- B. 18000
- C. 16000
- D. 1600
- Correct Answer
- 18000
ExplanationTotal number of letters = 8
Number of vowels = 3 and r occurs twice.
Total number of arrangements when there is no restriction = 8!/2!
When three vowels are together, regarding them as one letter, we have only 5 + 1 = 6 letters
These six letters can be arranged in 6!/2! ways, since r occurs twice.
But the three vowels can be arranged among themselves in 3! ways.
Hence number of arrangement when the three vowels are together = 6! /(2 !x 3!)
? Required number = 8!/2! - {6! / (2! x 3!)} = 18,000 - 1. Vowels being never together.
Options- A. 36 ways
- B. 84 ways
- C. 120 ways
- D. 10 ways Discuss
- 2. Vowels occupying odd places .
Options- A. 12 ways
- B. 16 ways
- C. 6 ways
- D. 20 ways Discuss
- 3. E being always in the middle.
Options- A. 18 ways
- B. 24 ways
- C. 48 ways
- D. 20 ways Discuss
- 4. O and A occupying end places.
Options- A. 12
- B. 14
- C. 20
- D. 18 Discuss
- 5. In how many ways, can 15 people be seated around two round tables with seating capacities of 7 and 8 people?
Options- A. 15!/(8!)
- B. 7!/88!
- C. 15C8 x 6! x 7!
- D. 15C8 x 8! Discuss
- 6. A mixed doubles tennis game is to be played between two teams ( each team consists of one male and one female). There are four married couples. No team is to consist of a husband and his wife. What is the maximum number of games that can be played?
Options- A. 12
- B. 48
- C. 36
- D. 42 Discuss
- 7. There is a 7-digit telephone number with all different digits. If the digit at extreme right and extreme left are 5 and 6 respectively, find how many such telephone number are possible?
Options- A. 120
- B. 100000
- C. 6720
- D. 30240 Discuss
- 8. In how many ways, can 24 persons be seated around a circular table if there are is 13 seats?
Options- A. 24! / [13 x 11! ]
- B. 22! / [14 x 12!]
- C. 23! / [13 x 11!]
- D. 24! / [12 x 12!] Discuss
- 9. There are 14 points in a plane, out of which 4 are collinear. Find the number of triangles made by these points .
Options- A. 364
- B. 360
- C. 368
- D. 365 Discuss
- 10. A question paper consists of two sections having respectively 3 and 5 questions. The following note is given on the paper. "It is not necessary to attempt all the question". One question from each section is compulsory. In how many ways, a candidate can select the question?
Options- A. 38
- B. 217
- C. 256
- D. 320 Discuss
Permutation and Combination problems
Search Results
Correct Answer: 84 ways
Explanation:
Total number of words = 5! = 120
combining the vowels at one place(OEA) with remaining 2 letters MG, letters can be arranged in 3! ways. Also, three vowels can be arranged in 3! ways
So, when vowels are together, then number of words = 3! x 3! = 36
there4; Required number of ways, when vowels being never together =120 - 36 = 84
Correct Answer: 12 ways
Explanation:
Three vowels (O, E, A) can be arranged in the odd places in 3! ways (1st position, 3rd position, 5th position) and two consonant (M, G) can be arranged in the even place in 2! ways (2nd place and 4th place).
? Total number of ways = 3! X 2! = 12
Correct Answer: 24 ways
Explanation:
When E is fixed in the middle, then there are four places left to be filled by four remaining letters O, M, G and A and this can be done in 4! ways.
? Total number of ways = 4! = 24
Correct Answer: 12
Explanation:
When O and A occupy end places. Then, the three letters (M, E, G) can be arranged themselves by 3! = 6 ways and two letters (O, A) can be arranged among themselves in 2! = 2 ways.
? Total number of ways = 6 x 2 = 12
Correct Answer: 15C8 x 6! x 7!
Explanation:
Number of ways in which 8 persons can be selected from 15 persons = 15C8
Now, 8 persons can be seated around a circular table in 7! ways.
Now, remaining 7 persons can be seated around a circular table in 6! ways.
? Required number of ways = 15C8 x 7! x 6!
Correct Answer: 48
Explanation:
Married couples :
MF MF MF MF ? AB, CD, EF, CD
Possible teams :
AD CB EB GB
AF CF ED GD
AH CH EH GF
Team AD can play only with CB, CF, CH, EB, EH, GB, GF (7 teams).
Teams AD cannot play with AF, AH, ED and GD.
The same will apply with all teams, So, number of total matches = 12 x 7 = 84
But every match includes 2 teams, so the actual number of matches = 84/2 = 48
Correct Answer: 6720
Explanation:
There is a 7 - digit telephone number but extreme right and extreme left positions are fixed .
i. e. , 6 x x x x x 5
? Required number of ways = 8 x 7 x 6 x 5 x 4 = 6720
Correct Answer: 24! / [13 x 11! ]
Explanation:
First , we select 13 persons out of 24 persons in 24 C13 ways.
Now, these 13 persons can be seated in 12! ways around a table .
So required number of ways = 24 C13 x 12!
= [24! / {13!(24 - 13)!}] x 12!
= [24! / {13! x 11!}] x 12!
= 24! / (13 x 11!)
Correct Answer: 360
Explanation:
The required number of triangles = nC3 - mC3
Here, n = 14, m = 4
= 14C3 - 4C3
= (14 x 13 x 12 x 11! ) / (3! x 11!) - 4! / (3! x 1!)
= (14 x 13 x 12)/6 - 4/1
= 14 x 26 - 4
= 364 - 4
= 360
Correct Answer: 217
Explanation:
Here, we have two sections A and B. Section A has 3 question and B has 5 question and one question from each section is compulsory according to the given condition.
? Number of ways selecting one or more than one question from section A
= 23 - 1 = 7
Similarly, from section B = 25 - 1 = 31
According to the rule of multiplication, the required number of ways in which a candidate can select the question
= 7 x 31 = 217
Comments
There are no comments.More in Aptitude:
Programming
Copyright ©CuriousTab. All rights reserved.