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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 00, 11, 22, 33 and 44 (where repetition of digits is not allowed).

Question: What is the probability that the number selected does not contain zero at any position ?

Options

  1. A0⋅120\cdot12
  2. B0⋅250\cdot25
  3. C0⋅3750\cdot375
  4. D0⋅450\cdot45

Correct answer

B. 0⋅250\cdot25

Step-by-step solution

The total number of 44-digit numbers formed using the digits 0,1,2,3,40, 1, 2, 3, 4 without repetition is calculated by filling the thousands place in 44 ways (excluding 00) and the remaining 33 places in ^{4}P_{3}ways.<br><br>Totaloutcomes=4×4×3×2=96ways.<br><br>Total outcomes = 4 \times 4 \times 3 \times 2 = 96

The number of 44-digit numbers formed without using 00 at any position means using only the digits 1,2,3,41, 2, 3, 4.

Favorable outcomes = ^{4}P_{4} = 4 \times 3 \times 2 \times 1 = 24<br><br>Requiredprobability=2496=14=0.25<br><br>Required probability = \dfrac{24}{96} = \dfrac{1}{4} = 0.25

Answer: 0⋅250\cdot25
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