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Permutations and Combinations

JEE Main 2025 (Online) 28th January Evening ShiftNumericalMedium📈 Topic in 21% papers+4
Ques. 1JEE Main 2025, 28 January (Evening Shift)

The number of natural numbers, between 212 and 999, such that the sum of their digits is 15, is .

Answer

64

Solution

Let the number be abc, 1 a 9, 0 b, c 9, b + c = 15 - a.

Number of pairs (b, c) with b + c = s: s + 1 if s 9, 19 - s if s 9.

a = 1 (s = 14): 5; a = 2 (s = 13): 6; a = 3 (s = 12): 7

a = 4 (s = 11): 8; a = 5 (s = 10): 9; a = 6 (s = 9): 10

a = 7 (s = 8): 9; a = 8 (s = 7): 8; a = 9 (s = 6): 7

Total from 100 to 999 = 69

Numbers ≤ 212 with digit sum 15: all 5 with a = 1 (159, 168, 177, 186, 195); for a = 2 the smallest is 249 > 212.

required number = 69 - 5 = 64

Answer: 64

Keep practising — Permutations and Combinations

Ques. 2JEE Main 2025, 24 January (Morning Shift)

Let S=\p1,p2 ,p10\ be the set of first ten prime numbers. Let A=S P, where P is the set of all possible products of distinct elements of S. Then the number of all ordered pairs (x,y), x S, y A, such that x divides y, is .

Ques. 3JEE Main 2025, 24 January (Morning Shift)

The number of 3-digit numbers, that are divisible by 2 and 3, but not divisible by 4 and 9, is .

Ques. 4JEE Main 2025, 24 January (Evening Shift)

Group A consists of 7 boys and 3 girls, while group B consists of 6 boys and 5 girls. The number of ways, 4 boys and 4 girls can be invited for a picnic if 5 of them must be from group A and the remaining 3 from group B, is equal to :

  1. 8925
  2. 9100
  3. 8575
  4. 8750
Ques. 5JEE Main 2025, 23 January (Morning Shift)

The number of words, which can be formed using all the letters of the word "DAUGHTER", so that all the vowels never come together, is :

  1. 34000
  2. 37000
  3. 35000
  4. 36000
Ques. 6JEE Main 2025, 23 January (Evening Shift)

The number of ways, 5 boys and 4 girls can sit in a row so that either all the boys sit together or no two boys sit together, is .

Ques. 7JEE Main 2025, 22 January (Morning Shift)

From all the English alphabets, five letters are chosen and are arranged in alphabetical order. The total number of ways, in which the middle letter is ' M ', is :

  1. 6084
  2. 5148
  3. 14950
  4. 4356
Ques. 8JEE Main 2025, 22 January (Evening Shift)

In a group of 3 girls and 4 boys, there are two boys B1 and B2. The number of ways, in which these girls and boys can stand in a queue such that all the girls stand together, all the boys stand together, but B1 and B2 are not adjacent to each other, is :

  1. 120
  2. 96
  3. 72
  4. 144
Ques. 9JEE Main 2024, 9 April (Evening Shift)

The number of integers, between 100 and 1000 having the sum of their digits equal to 14, is .

Ques. 10JEE Main 2024, 8 April (Morning Shift)

The number of 3-digit numbers, formed using the digits 2, 3, 4, 5 and 7, when the repetition of digits is not allowed, and which are not divisible by 3 , is equal to .

Ques. 11JEE Main 2024, 8 April (Evening Shift)

The number of ways five alphabets can be chosen from the alphabets of the word MATHEMATICS, where the chosen alphabets are not necessarily distinct, is equal to:

  1. 179
  2. 177
  3. 175
  4. 181

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