Q1: Let S = {1, 2, 3, 4, 5, 6} and X be the set of all relations R from S to S that satisfy both the following properties:
i. R has exactly 6 elements.
ii. For each (a, b) ∈ R, we have |a - b| ≥ 2.
Let Y = {R ∈ X : The range of R has exactly one element} and
Z = {R ∈ X : R is a function from S to S}.
Let n(A) denote the number of elements in a set A.
If n(X) = mC₆, then the value of m is _____. [JEE Advanced 2024 Paper 2]
Ans: 20
|a - b| ≥ 2 or |b - a| = 2
Total:
a = 1, b = 3, 4, 5, 6 → 8
a = 2, b = 4, 5, 6 → 6
a = 3, b = 5, 6 → 4
a = 4, b = 6 → 2
Sum = 20
n(X) = ²⁰C₆ = ᵐC₆
m = 20
Q2: Let S = {1, 2, 3, 4, 5, 6} and X be the set of all relations R from S to S that satisfy both the following properties:
i. R has exactly 6 elements.
ii. For each (a, b) ∈ R, we have |a - b| ≥ 2.
Let Y = {R ∈ X : The range of R has exactly one element} and
Z = {R ∈ X : R is a function from S to S}.
Let n(A) denote the number of elements in a set A.
If the value of n(Y) + n(Z) is k², then |k| is _______. [JEE Advanced 2024 Paper 2]
Ans: 36
Given |a - b| ≥ 2, so if
a = 1, b = 3, 4, 5, 6 → 4 × 2 = 8
a = 1, b = 4, 5, 6 → 3 × 2 = 6
a = 1, b = 5, 6 → 2 × 2 = 4
a = 1, b = 6 → 2 × 1 = 2
Total = 20
i.e. Total elements in X is ²⁰C₆
Now for n(Y), the range of R has exactly one element, i.e., second elements must be constant in R. Since R must have 6 elements, it is not possible to satisfy both conditions, so n(Y) = 0.
For n(Z):
1 → 3, 4, 5, 6
2 → 4, 5, 6
3 → 1, 5, 6
4 → 1, 2, 6
5 → 1, 2, 3
6 → 1, 2, 3, 4
Number of relations that are functions will be:
= ⁴C₁ × ³C₁ × ³C₁ × ³C₁ × ³C₁ × ⁴C₁
= (4 × 3 × 3)² = k²
i.e., k = 36
Q3: A group of 9 students, s₁, s₂, ..., s₉, is to be divided to form three teams X, Y, and Z of sizes 2, 3, and 4, respectively. Suppose that s₁ cannot be selected for the team X, and s₂ cannot be selected for the team Y. Then the number of ways to form such teams is __________. [JEE Advanced 2024 Paper 1]
Ans: 665
Given Data:
x | y | z |
---|---|---|
2 | 3 | 4 |
S₁̅ | S₂̅ |
C-i) When x does not contain S₁, but contains S₂
7C₁ × 7!3!4! = 245
C-ii) When x does not contain S₁, S₂ and y does not contain S₂
i.e. 7C₂ × 6!3!3! = 420
So total number of ways = 665.
Q1: Consider 4 boxes, where each box contains 3 red balls and 2 blue balls. Assume that all 20 balls are distinct. In how many different ways can 10 balls be chosen from these 4 boxes so that from each box at least one red ball and one blue ball are chosen ?
(a) 21816
(b) 85536
(c) 12096
(d) 156816 [JEE Advanced 2022 Paper 2]
Ans: (a)
Q2: The number of 4-digit integers in the closed interval [2022, 4482] formed by using the digits 0, 2, 3, 4, 6, 7 is _________. [JEE Advanced 2022 Paper 1]
Ans: 569
This is a 4-digit integer whose 0th digit called D, 10th digit called C, 100th digit called B and 1000th digit called A.
Given range for possible number is 2022 to 4482.
So, position A can have digits 2, 3 or 4.
0, 6 and 7 can't put in A as number starts with 0, 6 or 7 don't fall in the range between 2022 to 4482.
So, Position A can be filled with 2, 3 or 4 in 3C1=3 ways.
Position B can be filled by one of 0, 2, 3, 4, 6, 7
So, total possible ways for position B = 6C1=6 ways
Similarly, Position C can be filled in 6C1=6 ways
Position D can be filled in 6C1=6 ways
∴ Total possible integer numbers starting with 2 or 3 or 4
= 3 × 6 × 6 × 6 = 3 × 216 = 648
Now lets find those numbers which starts with 2 and 4 but don't fall in the range between 2022 to 4482.
Situation 1:
∴ Total possible numbers starting with 200 are = 6
Situation 2:
∴ Total possible number in this case = 1
Situation 3:
Total numbers in this case = 2 × 6 × 6 = 72
∴ Total number that don't fall in the range 2022 to 4482 which starts with 2 or 4 are
= 6 + 1 + 72=79
∴ Total numbers falls in the range 2022 to 4482
=648 − 79
=569
Q2: In a hotel, four rooms are available. Six persons are to be accommodated in these four rooms in such a way that each of these rooms contains at least one person and at most two persons. Then the number of all possible ways in which this can be done is .......... [JEE Advanced 2020 Paper 2]
Ans: 1080
The groups of persons can be made only in 2, 2, 1, 1
∴ So the number of required ways is equal to number of ways to distribute the 6 distinct objects in group sizes 1, 1, 2 and 2
=
= 360 x 3 = 1080
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JEE Advanced Previous Year Questions (2018 - 2024): Permutations and Combinations
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Q1: Let |X| denote the number of elements in a set X. Let S = {1, 2, 3, 4, 5, 6} be a sample space, where each element is equally likely to occur. If A and B are independent events associated with S, then the number of ordered pairs (A, B) such that 1 ≤ |B| < |A|, equals ............. [JEE Advanced 2019 Paper 2]
Ans: 1523
Given sample space S = {1, 2, 3, 4, 5, 6} and let there are i elements in set A and j elements in set B.
Now, according to information 1 ≤ j < i ≤ 6.
When number of element in set B = 1 then number of elements in set A can be 2 or 3 or 4 or 5 or 6. Number of such pairs of A and B in this case
= 6C1[6C2 + 6C3 + 6C4 + 6C5 + 6C6]
When number of element in set B = 2 then number of elements in set A can be 3 or 4 or 5 or 6. Number of such pairs of A and B in this case
= 6C2[ 6C3 + 6C4 + 6C5 + 6C6]
When number of element in set B = 3 then number of elements in set A can be 4 or 5 or 6. Number of such pairs of A and B in this case
= 6C3[ 6C4 + 6C5 + 6C6]
When number of element in set B = 4 then number of elements in set A can be 5 or 6. Number of such pairs of A and B in this case
= 6C4[ 6C5 + 6C6]
When number of element in set B = 5 then number of elements in set A can be 6. Number of such pairs of A and B in this case
= 6C5[ 6C6]
So, total number of ways of choosing sets A and B
= 6C1[6C2 + 6C3 + 6C4 + 6C5 + 6C6]
+ 6C2[ 6C3 + 6C4 + 6C5 + 6C6]
+ 6C3[ 6C4 + 6C5 + 6C6]
+ 6C4[ 6C5 + 6C6]
+ 6C5[ 6C6]
= Sum of all possible products of two terms from
6C1, 6C2, 6C3, ......., 6C6 = p(Assume)
Now we know,
(6C1 + 6C2 + .....+ 6C6)2
= [ (6C1)2 + (6C2)2+ ....+ (6C6)2] + 2[6C16C2 + 6C16C3 + ... +6C16C6
+ 6C26C3 + 6C26C4 + ... +6C26C6+ ....+ 6C56C6]
⇒ (6C1 + 6C2 + .....+ 6C6)2
= [ (6C1)2 + (6C2)2+ ....+ (6C6)2] + 2(p)
⇒ (26 - 6C0)2 = [ 12C6 - (6C0)2 ] + 2p
Q2: Let α and β be the roots of x2 − x − 1 = 0, with α > β. For all positive integers n, define
Then which of the following options is/are correct?
(a)
(b) bn = αn + βn for all n ≥ 1
(c) a1 + a2 + a3 + ... + an = an+2 − 1 for all n ≥ 1
(d) [JEE Advanced 2019 Paper 1]
Ans: (b), (c) & (d)
Given quadratic equation
x2 − x − 1 = 0, with α > β
So,
and
So, option (b) is correct.
Now,
= 12/89
So, option (a) is not correct.
On adding, we get
So, option (c) is also correct.
And Now,
Hence, options (b), (c) and (d) are correct.
Q1: In a high school, a committee has to be formed from a group of 6 boys M1, M2, M3, M4, M5, M6 and 5 girls G1, G2, G3, G4, G5.
(i) Let α1 be the total number of ways in which the committee can be formed such that the committee has 5 members, having exactly 3 boys and 2 girls.
(ii) Let α2 be the total number of ways in which the committee can be formed such that the committee has at least 2 members, and having an equal number of boys and girls.
(iii) Let α3 be the total number of ways in which the committee can be formed such that the committee has 5 members, at least 2 of them being girls.
(iv) Let α4 be the total number of ways in which the committee can be formed such that the committee has 4 members, having at least 2 girls such that both M1 and G1 are NOT in the committee together.
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