Discussion
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- Question
On the occasion of New Year, each student of a class sends greeting cards to the others. If there are 21 students in the class, what is the total number of greeting cards exchanged by the students?
Options- A. 380
- B. 420
- C. 441
- D. 400
- Correct Answer
- 420
ExplanationGiven total number of students in the class = 21
So each student will have 20 greeting cards to be send or receive (21 - 1(himself))
Therefore, the total number of greeting cards exchanged by the students = 20 x 21 = 420.
- 1. How many six digit odd numbers can be formed from the digits 0, 2, 3, 5, 6, 7, 8, and 9 (repetition not allowed)?
Options- A. 8640
- B. 720
- C. 3620
- D. 4512 Discuss
- 2. In a box, there are 5 black pens, 3 white pens and 4 red pens. In how many ways can 2 black pens, 2 white pens and 2 red pens can be chosen?
Options- A. 180
- B. 220
- C. 240
- D. 160 Discuss
- 3. The number of ways that 7 teachers and 6 students can sit around a table so that no two students are together is
Options- A. 7! x 7!
- B. 7! x 6!
- C. 6! x 6!
- D. 7! x 5! Discuss
- 4. To fill 8 vacancies there are 15 candidates of which 5 are from ST. If 3 of the vacancies are reserved for ST candidates while the rest are open to all, Find the number of ways in which the selection can be done ?
Options- A. 7920
- B. 74841
- C. 14874
- D. 10213 Discuss
- 5. Nine different letters of alphabet are given, words with 5 letters are formed from these given letters. Then, how many such words can be formed which have at least one letter repeated ?
Options- A. 43929
- B. 59049
- C. 15120
- D. 0 Discuss
- 6. From a bunch of flowers having 16 red roses and 14 white roses, four flowers have to be selected. In how many different ways can they be selected such that at least one red rose is selected?
Options- A. 27405
- B. 26584
- C. 26585
- D. 27404 Discuss
- 7. A card is drawn from a pack of 52 cards. What is the probability that either card is black or a king?
Options- A. 15/52
- B. 17/26
- C. 13/17
- D. 15/26 Discuss
- 8. In how many different ways can the letters of the word 'RITUAL' be arranged?
Options- A. 720
- B. 5040
- C. 360
- D. 180 Discuss
- 9. A Committee of 5 persons is to be formed from a group of 6 gentlemen and 4 ladies. In how many ways can this be done if the committee is to be included atleast one lady?
Options- A. 123
- B. 113
- C. 246
- D. 945 Discuss
- 10. In how many ways the letters of the word 'DESIGN' can be arranged so that no consonant appears at either of the two ends?
Options- A. 240
- B. 72
- C. 48
- D. 36 Discuss
Permutation and Combination problems
Search Results
Correct Answer: 8640
Correct Answer: 180
Explanation:
Number of ways of choosing 2 black pens from 5 black pens in ways.
Number of ways of choosing 2 white pens from 3 white pens in ways.
Number of ways of choosing 2 red pens from 4 red pens in ways.
By the Counting Principle, 2 black pens, 2 white pens, and 2 red pens can be chosen in 10 x 3 x 6 =180 ways.
Correct Answer: 7! x 6!
Explanation:
The students should sit in between two teachers. There are 7 gaps in between teachers when they sit in a roundtable. This can be done in ways. 7 teachers can sit in (7-1)! ways.
Required no.of ways is =
Correct Answer: 7920
Explanation:
ST candidates vacancies can be filled by ways = 10
Remaining vacancies are 5 that are to be filled by 12
=> = (12x11x10x9x8)/(5x4x3x2x1) = 792
Total number of filling the vacancies = 10 x 792 = 7920
Correct Answer: 43929
Explanation:
Number of words with 5 letters from given 9 alphabets formed =
Number of words with 5 letters from given 9 alphabets formed such that no letter is repeated is =
Number of words can be formed which have at least one letter repeated =
= 59049 - 15120
= 43929
Correct Answer: 27404
Explanation:
Given total 16 Red roses and 14 White roses = 30 roses
Four flowers have to be selected from 30 i.e, = 27405 Ways
Now, atleast one Red rose is selected i.e, 27405(total) - 1(all four are white roses) = 27404 ways.
Correct Answer: 15/26
Explanation:
Number of cards in a pack of cards = 52
Number of black cards = 26
Number of king cards = 4 (2 Red, 2 Black)
Required, the probability that if a card is drawn either card is black or a king =
Correct Answer: 720
Explanation:
The number of letters in the given word RITUAL = 6
Then,
Required number of different ways can the letters of the word 'RITUAL' be arranged = 6!
=> 6 x 5 x 4 x 3 x 2 x 1 = 720
Correct Answer: 246
Explanation:
A Committee of 5 persons is to be formed from 6 gentlemen and 4 ladies by taking.
(i) 1 lady out of 4 and 4 gentlemen out of 6
(ii) 2 ladies out of 4 and 3 gentlemen out of 6
(iii) 3 ladies out of 4 and 2 gentlemen out of 6
(iv) 4 ladies out of 4 and 1 gentlemen out of 6
In case I the number of ways = = 4 x 15 = 60
In case II the number of ways = = 6 x 20 = 120
In case III the number of ways = = 4 x 15 = 60
In case IV the number of ways = = 1 x 6 = 6
Hence, the required number of ways = 60 + 120 + 60 + 6 = 246
Correct Answer: 48
Explanation:
DESIGN = 6 letters
No consonants appear at either of the two ends.
= = 2 x 4 x 3 x 2 x 1= 48
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