Pocket Gems interview questions

It was a one hour interview. With three questions. The interviewer seemed very disinterested. Neways they asked me 3 questions. First one was reverse a string. I did in place reverse using single for loop. 2nd one was a trick but popular question. 10 jars with 100marbles each. On jar has marbles weighing 1.1g others 1g. Find out which jar it is and in minimum number of comparisons. I knew the answer was one but forgot the methodology. Next one was find the least common ancestor of a binary tree(bot binary search tree).