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
A.
Step-by-step solution
Total number of 4-digit numbers formed using without repetition:
The thousands place can be filled in ways (excluding ).
The remaining places can be filled in ways.
Total numbers .
For the number to be divisible by , the units digit must be , or .
Case 1: Units digit is .
The remaining places can be filled in ways.
Case 2: Units digit is or .
The units place can be filled in ways.
The thousands place can be filled in ways (excluding and the units digit).
The remaining places can be filled in ways.
Number of such numbers .
Total number of even 4-digit numbers .
Required probability .
Answer:
The thousands place can be filled in ways (excluding ).
The remaining places can be filled in ways.
Total numbers .
For the number to be divisible by , the units digit must be , or .
Case 1: Units digit is .
The remaining places can be filled in ways.
Case 2: Units digit is or .
The units place can be filled in ways.
The thousands place can be filled in ways (excluding and the units digit).
The remaining places can be filled in ways.
Number of such numbers .
Total number of even 4-digit numbers .
Required probability .
Answer: