Q253 / 270 · NDA 2026 (Phase 1) · Mathematics
Passage: A 4-digit number is selected at random formed by using the digits $0$, $1$, $2$, $3$ and $4$ (where repetition of digits is not allowed).
Question: What is the probability that the number selected is divisible by $4$ ?
Question: What is the probability that the number selected is divisible by $4$ ?
- A$\dfrac{1}{2}$
- B$\dfrac{7}{16}$
- C$\dfrac{9}{16}$
- Correct answerD$\dfrac{5}{16}$
Solution
Total number of $4$-digit numbers formed using $0, 1, 2, 3, 4$ without repetition:
The thousands place can be filled in $4$ ways (excluding $0$).
The remaining $3$ places can be filled in $^{4}P_{3} = 24$ ways.
Total possible numbers = $4 \times 24 = 96$.
A number is divisible by $4$ if the number formed by its last two digits is divisible by $4$.
The possible last two digits from the given set are $04, 12, 20, 24, 32, 40$.
Case 1: Last two digits are $04, 20$, or $40$ ($3$ cases).
Since $0$ is used, the first two places can be filled from the remaining $3$ digits in $^{3}P_{2} = 6$ ways.
Number of such numbers = $3 \times 6 = 18$.
Case 2: Last two digits are $12, 24$, or $32$ ($3$ cases).
Since $0$ is not used in the last two digits, the thousands place cannot be $0$. It can be filled in $2$ ways.
The hundreds place can be filled in $2$ ways.
Number of such numbers = $3 \times (2 \times 2) = 12$.
Total numbers divisible by $4 = 18 + 12 = 30$.
Required probability = $\dfrac{30}{96} = \dfrac{5}{16}$.
Answer: $\dfrac{5}{16}$
The thousands place can be filled in $4$ ways (excluding $0$).
The remaining $3$ places can be filled in $^{4}P_{3} = 24$ ways.
Total possible numbers = $4 \times 24 = 96$.
A number is divisible by $4$ if the number formed by its last two digits is divisible by $4$.
The possible last two digits from the given set are $04, 12, 20, 24, 32, 40$.
Case 1: Last two digits are $04, 20$, or $40$ ($3$ cases).
Since $0$ is used, the first two places can be filled from the remaining $3$ digits in $^{3}P_{2} = 6$ ways.
Number of such numbers = $3 \times 6 = 18$.
Case 2: Last two digits are $12, 24$, or $32$ ($3$ cases).
Since $0$ is not used in the last two digits, the thousands place cannot be $0$. It can be filled in $2$ ways.
The hundreds place can be filled in $2$ ways.
Number of such numbers = $3 \times (2 \times 2) = 12$.
Total numbers divisible by $4 = 18 + 12 = 30$.
Required probability = $\dfrac{30}{96} = \dfrac{5}{16}$.
Answer: $\dfrac{5}{16}$
Hence, the correct answer is option: 'D'.