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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 is divisible by 44 ?

Options

  1. A12\dfrac{1}{2}
  2. B716\dfrac{7}{16}
  3. C916\dfrac{9}{16}
  4. D516\dfrac{5}{16}

Correct answer

D. 516\dfrac{5}{16}

Step-by-step solution

Total number of 44-digit numbers formed using 0,1,2,3,40, 1, 2, 3, 4 without repetition:

The thousands place can be filled in 44 ways (excluding 00).

The remaining 33 places can be filled in ^{4}P_{3} = 24ways.<br><br>Totalpossiblenumbers=4×24=96ways.<br><br>Total possible numbers = 4 \times 24 = 96.

A number is divisible by 44 if the number formed by its last two digits is divisible by 44.

The possible last two digits from the given set are 04,12,20,24,32,4004, 12, 20, 24, 32, 40.

Case 1: Last two digits are 04,2004, 20, or 4040 (33 cases).

Since 00 is used, the first two places can be filled from the remaining 33 digits in ^{3}P_{2} = 6ways.<br><br>Numberofsuchnumbers=3×6=18ways.<br><br>Number of such numbers = 3 \times 6 = 18.

Case 2: Last two digits are 12,2412, 24, or 3232 (33 cases).

Since 00 is not used in the last two digits, the thousands place cannot be 00. It can be filled in 22 ways.

The hundreds place can be filled in 22 ways.

Number of such numbers = 3×(2×2)=123 \times (2 \times 2) = 12.

Total numbers divisible by 4=18+12=304 = 18 + 12 = 30.

Required probability = 3096=516\dfrac{30}{96} = \dfrac{5}{16}.

Answer: 516\dfrac{5}{16}
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