If the papers of 4 students can be checked by any one of the 7 teachers, then the probability that all the 4 papers are checked by exactly 2 teachers, is equal to

Step-by-step solution

Total ways in which papers can be checked is equal 7 4 . Now, two teachers who have to check all the papers can be selected in C 2 7 ways and papers can be checked by them is 2 4 - 2 favourable ways. Thus, required probability = C 2 7 2 4 - 2 7 4 = 6 49