For each question on a multiplechoice test there are five po

For each question on a multiple-choice test, there are five possible answers of which exactly one is correct. Suppose that there are 15 questions and the passing grade is 9 or more. If a student selects answer at random, what is the probability that the third question answered correctly is question 7? 0.0492 0.0688 0.0989 0.1406 0.2500

Solution

The question number 7 is the third correct answer implies that there are 4 incorrect answers of the 6 questions already answered, or 2 correct answeres out of first 6 questions.

These two questions can be aby, the number of ways in which this can happen is 6C2=15

Also as there are 5 choices, so probability of correct option is 0.2, while probability of wrong answer is 0.8

Hence the required probability is 15(0.2)^3(0.8)^4=0.0492

Hence option A is correct option