Qualcomm Design Engineer interview questions

It was through campus recruitment. They had two technical rounds. I cleared the first roud but was rejected in the second. In the first round they asked questions based on Finite State Machines. Also a simple digital circuit and it's truth table. Also I was asked to design an N-MOS inverter. There was also a puzzle - if there are 21 balls with only one weighing heavier, how will you find it using only one weighing balance in the minimum number of weighings? In my second round I was asked to design the FSM for a Vending Machine. And then they asked me to solve a timing analysis question which I couldn't. It was a little complex involving setup and hold time.