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Quantitative Aptitude

PERMUTATION AND COMBINATION MCQs

Permutations And Combinations

Total Questions : 444 | Page 38 of 45 pages
Question 371. There are 10 seats around a circular table. If 8 men and 2 women have to seated around a circular table, such that no two women have to be separated by at least one man. If P and Q denote the respective number of ways of seating these people around a table when seats are numbered and unnumbered, then P : Q equals
  1.    9 : 1
  2.    72 : 1
  3.    10 : 1
  4.    8 : 1
 Discuss Question
Answer: Option C. -> 10 : 1
Initially we look at the general case of the seats not numbered.
The total number of cases of arranging 8 men and 2 women, so that women are together,
⇒ 8! ×2!
The number of cases where in the women are not together,
⇒ 9! - (8! × 2!) = Q
Now, when the seats are numbered, it can be considered to a linear arrangement and the number of ways of arranging the group such that no two women are together is,
⇒ 10! - (9! × 2!)
But the arrangements where in the women occupy the first and the tenth chairs are not favorable as when the chairs which are assumed to be arranged in a row are arranged in a circle, the two women would be sitting next to each other.
The number of ways the women can occupy the first and the tenth position,
= 8! × 2!
The value of P = 10! - (9! × 2!) - (8! × 2!)
Thus P : Q = 10 : 1
Question 372. In how many different way can the letters of the word WEDDING be arranged?
  1.    2500
  2.    2520
  3.    5000
  4.    5040
  5.    NONE OF THESE
 Discuss Question
Answer: Option B. -> 2520
The given word contains 7 letters which D is taken 2 times.
∴ Required number of ways
$$\eqalign{
& = \frac{{7!}}{{2!}} \cr
& = \frac{{7 \times 6 \times 5 \times 4 \times 3 \times 2 \times 1}}{{2 \times 1}} \cr
& = 2520 \cr} $$
Question 373. In how many different ways can the letters of the word RIDDLED be arranged?
  1.    840
  2.    1680
  3.    2520
  4.    5040
  5.    None of these
 Discuss Question
Answer: Option A. -> 840
The given word contains 7 letters of which D is taken 3 times.
∴ Required number of ways
$$\eqalign{
& = \frac{{7!}}{{3!}} \cr
& = \frac{{7 \times 6 \times 5 \times 4 \times 3!}}{{3!}} \cr
& = \left( {7 \times 6 \times 5 \times 4} \right) \cr
& = 840 \cr} $$
Question 374. In how many different ways can the letters of the word AUCTION be arranged in such a way that the vowels always come together?
  1.    30
  2.    48
  3.    144
  4.    576
  5.    None of these
 Discuss Question
Answer: Option D. -> 576
The given word contains 7 different letters.
Keeping the vowels (AUIO) together, we take them as 1 letter.
Then, we have to arrange the letters CTN (AUIO).
Now, 4 letters can be arranged in 4! = 24 ways.
The vowels (AUIO) can be arranged among themselves in 4! = 24 ways.
∴ Required number of ways = (24 × 24) = 576
Question 375. A select group of 4 is to be formed from 8 men and 6 women in such a way that the group must have at least 1 women. In how many different ways can it be done ?
  1.    364
  2.    728
  3.    931
  4.    1001
  5.    None of these
 Discuss Question
Answer: Option C. -> 931
Required number of ways
$$ = \left( {{}^6{C_1} \times {}^8{C_3}} \right) + \left( {{}^6{C_2} \times {}^8{C_2}} \right)$$     $$ + \left( {{}^6{C_3} \times {}^8{C_1}} \right)$$   $$ + \left( {{}^6{C_4} \times {}^8{C_0}} \right)$$
$$ = \left\{ {6 \times \frac{{8 \times 7 \times 6}}{{3 \times 2 \times 1}}} \right\} + $$    $$\left( {\frac{{6 \times 5}}{{2 \times 1}} \times \frac{{8 \times 7}}{{2 \times 1}}} \right)$$   $$ + \left( {\frac{{6 \times 5 \times 4}}{{3 \times 2 \times 1}} \times 8} \right)$$    $$ + \left( {{}^6{C_2} \times 1} \right)$$
$$ = \left\{ {6 \times \frac{{8 \times 7 \times 6}}{{3 \times 2 \times 1}}} \right\}$$    $$ +\, 420\, + $$  $$\left( {\frac{{6 \times 5 \times 4}}{6} \times 8} \right)$$   $$ + \left( {\frac{{6 \times 5}}{{2 \times 1}} \times 1} \right)$$
$$ = \left( {336 + 420 + 160 + 15} \right)$$
$$ = 931$$
Question 376. In how many different ways can the letters of the word MACHINE be arranged so that the vowels may occupy only the odd positions?
  1.    210
  2.    576
  3.    144
  4.    1728
  5.    3456
 Discuss Question
Answer: Option B. -> 576
There are 7 letters in the given word, out of which there are 3 vowels and 4 consonants.
Let us mark the positions to be filled up as follows:
$$\left( {\mathop {}\limits^1 } \right)\left( {\mathop {}\limits^2 } \right)\left( {\mathop {}\limits^3 } \right)\left( {\mathop {}\limits^4 } \right)\left( {\mathop {}\limits^5 } \right)\left( {\mathop {}\limits^6 } \right)\left( {\mathop {}\limits^7 } \right)$$
Now, 3 vowels can placed at any of the three places out of four marked 1, 3, 5, 7
Number of ways of arranging the vowels
$$\eqalign{
& = {}^4{P_3} \cr
& = \left( {4 \times 3 \times 2} \right) \cr
& = 24 \cr} $$
4 consonants at the remaining 4 positions may be arranged in $${}^4{P_4} = 4! = $$  
24 ways
Required number of ways = (24 × 24) = 576
Question 377. In how many ways can the letters of the word ‘MOMENT’ be arranged?
  1.    360
  2.    60
  3.    720
  4.    120
 Discuss Question
Answer: Option A. -> 360
There are six letters in the given word MOMENT and letter 'M' has come twice.
∴ Required number of ways
$$\eqalign{
& = \frac{{6!}}{{2!}} \cr
& = \frac{{6 \times 5 \times 4 \times 3 \times 2 \times 1}}{{2 \times 1}} \cr
& = 360 \cr} $$
Question 378. A committee of 5 members is to be formed by selecting out of 4 men and 5 women. In how many different ways the committee can be formed if it should have at least 1 man?
  1.    115
  2.    120
  3.    125
  4.    140
  5.    None of these
 Discuss Question
Answer: Option C. -> 125
The committee should have
(1 man, 4 women) or (2 men, 3 women) or (3 men, 2 women) or ( 4 men, 1 woman)
Required number of ways
$$ = \left( {{}^4{C_1} \times {}^5{C_4}} \right) + \left( {{}^4{C_2} \times {}^5{C_3}} \right)$$      $$ + \left( {{}^4{C_3} \times {}^5{C_2}} \right)$$   $$ + \left( {{}^4{C_6} \times {}^5{C_1}} \right)$$
$$ = \left( {{}^4{C_1} \times {}^5{C_1}} \right) + \left( {{}^4{C_2} \times {}^5{C_2}} \right)$$      $$ + \left( {{}^4{C_1} \times {}^5{C_2}} \right)$$   $$ + \left( {{}^4{C_4} \times {}^5{C_1}} \right)$$
$$ = \left( {4 \times 5} \right) + \left( {\frac{{4 \times 3}}{{2 \times 1}} \times \frac{{5 \times 4}}{{2 \times 1}}} \right)$$      $$ + \left( {4 \times \frac{{5 \times 4}}{{2 \times 1}}} \right)$$   $$ + \left( {1 \times 5} \right)$$
$$ = \left( {20 + 60 + 40 + 5} \right)$$
$$ = 125$$
Question 379. In how many ways can the letters of the word MATHEMATICS be arranged so that all the vowels always come together?
  1.    10080
  2.    120960
  3.    4989600
  4.    21160
  5.    None of these
 Discuss Question
Answer: Option B. -> 120960
Keeping the vowels (AEIA) together, we have MTHMTCS (AEAI).
Now, we have to arrange 8 letters, out of which we have 2M, 2T and the rest are all different.
Number of ways of arranging these letters
$$\eqalign{
& = \frac{{8!}}{{2!.2!}} \cr
& = \frac{{8 \times 7 \times 6 \times 5 \times 4 \times 3 \times 2 \times 1}}{{2 \times 1 \times 2 \times 1}} \cr
& = 10080 \cr} $$
Now, (AEAI) has 4 letters, out of which we have 2A, 1E and 1I.
Number of ways of arranging these letters
$$\eqalign{
& = \frac{{4!}}{{2!}} \cr
& = \frac{{4 \times 3 \times 2 \times 1}}{2} \cr
& = 12 \cr} $$
∴ Required number of ways = (10080 × 12) = 120960
Question 380. In how many different ways can the letters of the word SOFTWARE be arranged in such a way that the vowels always come together?
  1.    120
  2.    360
  3.    1440
  4.    13440
  5.    4320
 Discuss Question
Answer: Option E. -> 4320
The given word contains 8 different letters.
We keep the vowels (OAE) together and treat them as 1 letter.
Thus, we have to arrange the 6 letters SFTWR(OAE)
These can be arranged in 6! = 720 ways
The vowels (OAE) can be arranged among themselves in 3! = 6 ways.
∴ Required number of ways = (720 × 6) = 4320

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