NDA 2026
- Exam
- NDA
- Year
- 2026
- Subject
- Mathematics
- Chapter
- Permutation and Combination
NDA 2026 · Mathematics · Permutation and Combination
Passage: A 4-digit number is selected at random formed by using the...
Passage: A 4-digit number is selected at random formed by using the digits , , , and (where repetition of digits is not allowed).
Question: What is the probability that the number selected is divisible by ?
Question: What is the probability that the number selected is divisible by ?
Options
- A
- B
- C
- D
Correct answer
D.
Step-by-step solution
Total number of -digit numbers formed using without repetition:
The thousands place can be filled in ways (excluding ).
The remaining places can be filled in ^{4}P_{3} = 24.
A number is divisible by if the number formed by its last two digits is divisible by .
The possible last two digits from the given set are .
Case 1: Last two digits are , or ( cases).
Since is used, the first two places can be filled from the remaining digits in ^{3}P_{2} = 6.
Case 2: Last two digits are , or ( cases).
Since is not used in the last two digits, the thousands place cannot be . It can be filled in ways.
The hundreds place can be filled in ways.
Number of such numbers = .
Total numbers divisible by .
Required probability = .
Answer:
The thousands place can be filled in ways (excluding ).
The remaining places can be filled in ^{4}P_{3} = 24.
A number is divisible by if the number formed by its last two digits is divisible by .
The possible last two digits from the given set are .
Case 1: Last two digits are , or ( cases).
Since is used, the first two places can be filled from the remaining digits in ^{3}P_{2} = 6.
Case 2: Last two digits are , or ( cases).
Since is not used in the last two digits, the thousands place cannot be . It can be filled in ways.
The hundreds place can be filled in ways.
Number of such numbers = .
Total numbers divisible by .
Required probability = .
Answer: