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- Question
- If there are 10 positive real numbers n 1 < n 2, n 3 .... < n 10 How many triplets of these numbers (n 1, n 2, n 3) (n 2, n 3, n 4), ... can be generated such that in each triplet the first number is always less than the second number and the second number is always less the third number?
Options- A. 45
- B. 90
- C. 120
- D. 180
- Correct Answer
- 120
ExplanationThree numbers can be selected and arranged out of 10 numbers in 10P3 ways 10!/7! = 10 x 9 x 8
Now, this arrangement is restricted to a given condition that first number is always less than the second number and second number is always than the third number. Thus, three numbers can be arranged among themselves in 3! ways.
Hence, required number of arrangement = (10 x 9 x 8)/(3 x 2)
= 120 ways - 1. A man has 5 friends and his wife has 4 friends. They want to invite either of their friends, one or more to a party. In how many ways can they do so?
Options- A. 9
- B. 18
- C. 31
- D. 46 Discuss
- 2. The total number of words, which can be formed out of the letters a, b, c, d, e, f taken 3 together, such that each word contains at least one vowel is?
Options- A. 72
- B. 48
- C. 96
- D. None of these Discuss
- 3. 4 boys and 2 girls are to be seated in a row in such a way that two girls are always together. In how many different ways can they be seated?
Options- A. 120
- B. 720
- C. 148
- D. 240 Discuss
- 4. A library has two books each having three copies and three other books each having two copies. In how many ways can all these books be arranged in a shelf so that copies of the same book are not separated?
Options- A. 120
- B. 180
- C. 160
- D. 140 Discuss
- 5. There are 20 books of which 4 are single volumes and the other are books of 8, 5 and 3 volumes respectively. In how many ways can all these books be arranged on a self so that volumes of the same book are not separated?
Options- A. 7! 8! 5! 3!
- B. 7! 8! 4! 3!
- C. 7! 6! 5! 3!
- D. None of these Discuss
- 6. How many three letter computer passwords can be formed (no repetition allowed) with at least one symmetric letter?
Options- A. 990
- B. 2730
- C. 12870
- D. 1560000 Discuss
- 7. A question paper had 10 questions. Each question could only be answered as True (T) or false (F). Each candidate answered all the questions. Yet, no two candidate wrote the answers in an identical sequence. How many different sequences of answers are possible?
Options- A. 20
- B. 40
- C. 512
- D. 1024 Discuss
- 8. Groups, each containing 3 boys are to be formed out of 5 boys, A, B , C, D and E such that no group can contain both C and D together. What is the maximum number of such different groups?
Options- A. 5
- B. 6
- C. 7
- D. 8 Discuss
- 9. In a question paper, there are four multiple choice type question. Each question has five choices with only one choice for its correct answer. What is the total number of ways in which a candidate will not get all the four answers correct?
Options- A. 19
- B. 120
- C. 624
- D. 1024 Discuss
- 10. In how many difference ways can six players be arranged in a line such that two of them, Abhinav and Manjesh are never together?
Options- A. 120
- B. 240
- C. 360
- D. 480 Discuss
Permutation and Combination problems
Search Results
Correct Answer: 46
Explanation:
Number of ways of selecting one or more friends from 5 friends
= 5C1 + 5C2 + 5C3 + 5C4 + 5C5
= 5 + 10 + 10 + 5 + 1
= 31 ways
Number of ways of selecting one or more friends from 4 friends = 4C1 + 4C2 + 4C3 + 4C4
= 4 + 6 + 4 + 1
= 15 ways
? Total number of ways = 31 + 15 = 46 ways
Correct Answer: 96
Explanation:
The required number of words is : (2C1 x 4C2 + 2C2 x 2C1) 3! = 96
Correct Answer: 240
Explanation:
Assume the 2 girl students to be together i,e (one). Now there are 5 students.
Possible ways of arranging them are 5! = 120
Now they (two girl) can arrange themselves in 2! ways.
Hence, total ways = 120 x 2! = 240
Correct Answer: 120
Explanation:
Regarding all copies of the same book as one book, we have only 5 books. These 5 books can be arranged in 5! ways. But all copies of the same book being identical can be arranged in only one way.
? Required number = 5! x 1! x 1! x 1! x 1! = 120
Correct Answer: 7! 8! 5! 3!
Explanation:
Volumes of the same book are not to be separated i, e. all volumes of the same book are to be kept together, Regarding all volumes of the same book as one book, we have only 4 + 1 + 1 + 1 = 7 books.
These seven books can be arranged in 7! ways. The book having 8 volumes can be arranged among themselves in 8! ways, the book having 5 volumes can be arranged among themselves in 5! ways, and the book having 3 volumes can be arranged among themselves in 3! ways.
? Required number = 7! 8! 5! 3!
Correct Answer: 12870
Explanation:
Total number of password using all alphabets -Total
number of password using no symmetric alphabets
= (26 x 25 x 24 ) - (15 x 14 x 13 )
= 12870
Correct Answer: 1024
Explanation:
Each question can be answered in 2 ways.
? 10 question can be answered = 210 = 1024 ways
Correct Answer: 7
Explanation:
Maximum number of such different groups = ABC , ABD, ABE, BCE, BDE, CEA, DEA = 7
Correct Answer: 624
Explanation:
No of multiple choice type questions = 4
Total number of ways = 5 x 5 x 5 x 5 = 625
Number of correct answer = 1
Number of false answers = 625 - 1 = 624
Correct Answer: 360
Explanation:
As, there are six players, so total ways in which they can be arranged = 6 ! ways
Also, two particular players,are never together.
? Required ways = 6!/2! = 360
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