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31
In how many different ways can the letters of the word AWARE be arranged?
Discuss
Answer & Solution
Answer: Option B
Solution:
The given word contains 5 letters of which A is taken 2 times.
∴ Required number of ways
$$\eqalign{ & = \frac{{5!}}{{2!}} \cr & = \frac{{5 \times 4 \times 3 \times 2 \times 1}}{2} \cr & = 60 \cr} $$
32
A committee of 5 members is to be formed out of 3 trainees, 4 professors and 6 research associate. In how many different ways can this be done if the committee should have 2 trainees and 3 research associates?
Discuss
Answer & Solution
Answer: Option C
Solution:
Required number of ways
$$\eqalign{ & = \left( {{}^3{C_2} \times {}^6{C_3}} \right) \cr & = \left( {{}^3{C_1} \times {}^6{C_3}} \right) \cr & = \left( {3 \times \frac{{6 \times 5 \times 4}}{{3 \times 2 \times 1}}} \right) \cr & = 60 \cr} $$
33
In how many different ways can the letters of the word CREAM be arranged?
Discuss
Answer & Solution
Answer: Option B
Solution:
The given word contains 5 letters, all different.
∴ Required number of ways
$$\eqalign{ & = 5! \cr & = \left( {5 \times 4 \times 3 \times 2 \times 1} \right) \cr & = 120 \cr} $$
34
In how many different ways can the letters of the word ALLAHABAD be arranged?
Discuss
Answer & Solution
Answer: Option C
Solution:
The given word contains 9 letters, namely 4A, 2L, 1H, 1B and 1D.
∴ Required number of ways
$$\eqalign{ & = \frac{{9!}}{{4! \,2! \,1! \,1! \,1!}} \cr & = \frac{{9 \times 8 \times 7 \times 6 \times 5 \times 4 \times 3 \times 2 \times 1}}{{4 \times 3 \times 2 \times 1 \times 2}} \cr & = 7560 \cr} $$
35
From a group of 7 men 6 women, 5 persons are to be selected to form a committee so that at least 3 men are there on the committee. In how many ways can it be done?
Discuss
Answer & Solution
Answer: Option D
Solution:
Required number of ways
$$ = \left( {{}^7{C_3} \times {}^6{C_2}} \right) + $$   $$\left( {{}^7{C_4} \times {}^6{C_1}} \right) + $$   $$\left( {{}^7{C_5} \times {}^6{C_0}} \right)$$
$$ = \left\{ {\frac{{7 \times 6 \times 5}}{{3!}} \times \frac{{6 \times 5}}{{2!}}} \right\}$$     $$ + \left( {{}^7{C_3} \times {}^6{C_1}} \right)$$   $$ + \left( {{}^7{C_2} \times 1} \right)$$
$$ = \left\{ {\frac{{7 \times 6 \times 5}}{6} \times \frac{{6 \times 5}}{{2 \times 1}}} \right\}$$     $$ + \left( {\frac{{7 \times 6 \times 5}}{{3 \times 2 \times 1}} \times 6} \right)$$    $$ + \left( {\frac{{7 \times 6}}{{2 \times 1}} \times 1} \right)$$
$$\eqalign{ & = \left( {525 + 210 + 21} \right) \cr & = 756 \cr} $$
36
In how many different ways can the letters of the word BANKING be arranged in such a way that the vowels always come together?
Discuss
Answer & Solution
Answer: Option E
Solution:
The given words contains 7 letters of which N is taken 2 times.
We keep the vowels (AI) together and treat them as 1 letter.
Thus, we have to arrange 6 letters BNKNG (AI) of which N occurs 2 times and rest are different.
These can be arranged in
$$\frac{6!}{2!}$$ = (6 × 5 × 4 × 3 ) = 360 days
Now 2 vowels (AI) can be arranged among themselves in 2 ways.
∴ Required number of ways = (360 × 2) = 720
37
A box contains 2 white, 3 black and 4 red balls. In how many ways can 3 balls be drawn from the box, if at least 1 black ball is to be included in the draw?
Discuss
Answer & Solution
Answer: Option C
Solution:
We may have (1 black and 2 non-black) or (2 black and 1 non-black) or (3 black).
Required number of ways
$$\eqalign{ & \left( {{}^3{C_1} \times {}^6{C_2}} \right) + \left( {{}^3{C_2} \times {}^6{C_1}} \right) + \left( {{}^3{C_3}} \right) \cr & = \left\{ {3 \times \frac{{6 \times 5}}{{2 \times 1}}} \right\} + \left( {\frac{{3 \times 2}}{{2 \times 1}} \times 6} \right) + 1 \cr & = \left( {45 + 18 + 1} \right) \cr & = 64 \cr} $$
38
Out of 5 men and 3 women, a committee of three members is to be formed so that it has 1 women, and 2 men. In how many different ways can it be done?
Discuss
Answer & Solution
Answer: Option D
Solution:
Required number of ways
$$\eqalign{ & = \left( {{}^3{C_1} \times {}^5{C_2}} \right) \cr & = 3 \times \frac{{5 \times 4}}{{2 \times 1}} \cr & = 30 \cr} $$
39
In how many different ways can the letters of the word BANANA be arranged?
Discuss
Answer & Solution
Answer: Option A
Solution:
The given words contains 6 letters of which A is taken 3 times, N is taken 2 times and the rest are all different.
∴ Required number of ways
$$\eqalign{ & = \frac{{6!}}{{3! \times 2!}} \cr & = \frac{{6 \times 5 \times 4 \times 3 \times 2 \times 1}}{{6 \times 2}} \cr & = 60 \cr} $$
40
A committee of 5 members is to be formed out of 3 trainees, 4 professors and 6 research associates. In how many different ways can this be done, if the committee should have 4 professors and 1 research associate or all 3 trainees and 2 professors?
Discuss
Answer & Solution
Answer: Option E
Solution:
Required number of ways
$$ = \left( {{}^4{C_4} \times {}^6{C_1}} \right) + $$   $$\left( {{}^3{C_3} \times {}^4{C_{2}}} \right)$$
$$\eqalign{ & = \left( {1 \times 6} \right) + \left( {1 \times \frac{{4 \times 3}}{2}} \right) \cr & = \left( {6 + 6} \right) \cr & = 12 \cr} $$