7 common mistakes in English #shorts

Class 12 Common Mistakes Done by Students

Most Common Mistakes To Avoid While Preparing for NEET || Major Mistakes || NEET 2020 Preparation

The probabilities of solving a problem correctly by A and B are (1)/(8) and (1)/(12) respectively. Given that they obtain the same answer after solving a problem and the probability of a common mistake by them is (1)/(1001) , then probability that their solution is correct is (Assuming that if they commit different mistake, then their answers will differ)

In how many can the lettes in English alphabet be arranged, so that there are 7 letters between the letters a and b.