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NCERT Solutions for class 11 Maths | Chapter 7 - Permutations and Combinations

(1) A five digit number divisible by 3 is to be formed using the numbers 0, 1, 2, 3, 4 and 5 without repetitions. The total number of ways this can be done is
[A] 216
[B] 600
[C] 240
[D] 3125
Answer: 216
(2) Total number of words formed by 2 vowels and 3 consonants taken from 4 vowels and 5 consonants is equal to
[A] 60
[B] 120
[C] 7200
[D] 720
Answer: 7200

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(3) The sum of the digits in unit place of all the numbers formed with the help of 3, 4, 5 and 6 taken all at a time is
[A] 432
[B] 108
[C] 36
[D] 18
Answer: 108
(4) The number of different four digit numbers that can be formed with the digits 2, 3, 4, 7 and using each digit only once is
[A] 120
[B] 96
[C] 24
[D] 100
Answer: 24
(5) The number of possible outcomes when a coin is tossed 6 times is
[A] 36
[B] 64
[C] 12
[D] 32
Answer: 64
(6) nC12 = nC8, then n is equal to
[A] 20
[B] 12
[C] 6
[D] 30
Answer: 20
(7) On a shelf, 2 books of Geology, 2 books of Sociology and 5 of Economics are to be arranged in such a way that the books of any subject are to be together. Find in how many ways can this be done?
[A] 3846
[B] 2880
[C] 900
[D] 90
Answer: 2880
(8) A person can go from place “P” to “Q” by 7 different modes of transport, but is allowed to return back to “P” by any mode other than the one used earlier. In how many different ways can he complete the entire journey?
[A] 42
[B] 30
[C] 56
[D] 65
Answer: 42
(9) A briefcase has a number-lock system containing a combination of 3 digits (Each digit can be of numbers 0 to 8). If the correct combination is unknown, how much maximum time would be required to open the bag if each “trial” of combination takes 3 seconds?
[A] 45.23 minutes
[B] 36.45 minutes
[C] 60.34 minutes
[D] 90.15 minutes
Answer: 36.45 minutes
(10) A box contains 2 white, 3 black and 5 red balls. In how many ways can three balls be drawn from the box if at least one black ball is to be included in the draw?
[A] 29
[B] 36
[C] 48
[D] 85
Answer: 85
(11) In how many different ways can the letters of the word ‘GEOMETRY’ be arranged so that the vowels always come together?
[A] 720
[B] 4320
[C] 2160
[D] 40320
Answer: 4320
(12) How many words can be formed by using all letters of word ALIVE.
[A] 86
[B] 95
[C] 105
[D] 120
Answer: 120
(13) How many 3-letter words can be formed out of the letters of the word ‘CORPORATION’, if repetition of letters is not allowed?
[A] 990
[B] 336
[C] 720
[D] 504
Answer: 336
(14) In a group containing 6 cows and 4 buffalos, 4 livestock are to be selected in such a way that at least 1 cow should always be present. How many way of doing that are possible?
[A] 209
[B] 205
[C] 194
[D] 163
Answer: 209
(15) In how many ways can the letters of the word INDIA be arranged, such that all vowels are never together?
[A] 48
[B] 42
[C] 28
[D] 36
Answer: 42
(16) In how many ways can the letters of the word ENCYCLOPAEDIA be arranged such that vowels only occupy the even positions?
[A] 453600
[B] 128000
[C] 478200
[D] 635630
Answer: 453600
(17) There are 35 people in a group. There are 12 school girls, 10 school boys, 5 senior citizens and 8 babies in the group. The organizer of the group wants to select a school girl or a school boy as leader of the group. In how many ways can he do so?
[A] 22
[B] 1/2
[C] 13
[D] 35
Answer: 22
(18) A bank has 6 digit account number with no repetition of digits within a account number. The first and last digit of the account numbers is fixed to be 4 and 7. How many such account numbers are possible?
[A] 10080
[B] 5040
[C] 890
[D] 1680
Answer: 1680
(19) A trekking group is to be formed having 6 members. They are to be selected from 3 girls, 4 boys and 5 teachers. In how many ways can the group be formed so that there are 3 teachers and 3 boys or 2 girls and 4 teachers?
[A] 55
[B] 90
[C] 27
[D] 144
Answer: 55
(20) In a class, there are 15 students. During a Christmas party all of them shook hands with each other only once. How many handshakes took place in the class?
[A] 120
[B] 210
[C] 105
[D] 55
Answer: 105

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