Q56 / 90 · JEE Main 2013 (07 Apr) · Mathematics

A multiple choice examination has 5 questions. Each question has three alternative answers out of which exactly one is correct. The probability that a student will get 4 or more correct answers just by guessing is :

  • Correct answer
    A
    1 1 3 5
  • B
    1 0 3 5
  • C
    1 7 3 5
  • D
    1 3 3 5

Solution

4 or more correct answers means and 1 or 0 wrong answers.
for 1 wrong questions  5 C 1 × 2 C 1 = 1 0

for 0 wrong questions =1

Hence favourable ways =11

Total ways of answering 35

Hence probability = 1 1 3 5

Hence, the correct answer is option: 'A'.

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