simple array qusetions

Two easy puzzles .. and my first post too.. baki uncles will be happy to see it finally ;)

1. you have a sorted array. it has been rotated at an unknown index.. suggest an algorithm to find out an element from the rotated array... ex.. the array 561234 was made by rotating 123456 at the 4th index.. so how would you go about finding any number from the rotated array?

2. you have an array of the form a0a1a2...anb0b1b2....bn . how will you convert it into a0b0a1b1..anbn?? use O(1) memory and ofcourse come up with an O(n) running time complexity solution

3. an array has n/2 unique elements and one other element which has been repeated n/2 times... suggest different ways to find the repeated element.. O(n) solution can be achieved in multiple ways