probability

In a multiple choice question, there are four alternatives, of which one or more are correct. A candidate will get marks in the question only if he ticks all the correct answers. If the candidate ticks the answers at random but is allowed upto three chances to answer the question, then the probability that he will get marks in the question is .......................

Answer:

All are correct == 1 way

Any 3 are correct == 4 ways

Any 2 are correct == 6 ways

Any 1 is correct == 4 ways

Total number of ways of getting the answer correct = 1 + 4 + 6 + 4 = 15

So, Probability of getting it right in one chance = 1/15

So, probability of getting it right in 3 chances = 3 x 1/15 = 1/5