JEE PYQ: Permutation And Combination Question 19
Question 19 - 2020 (04 Sep Shift 2)
A test consists of 6 multiple choice questions, each having 4 alternative answers of which only one is correct. The number of ways, in which a candidate answers all six questions such that exactly four of the answers are correct, is ______.
Show Answer
Answer: 135
Solution
Choose 4 correct questions: ${}^6C_4 = 15$. For each wrong question, 3 wrong choices: $3^2 = 9$. Total $= 15 \times 9 = 135$.
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