Citi Quantitative Analyst Programmer interview questions

Phone interview after school resume drop. Mostly simple probability/computer science questions; i.e: a) What is the variance of the sum of two rolls of a six sided die? b) Is this higher or lower than the variance of double the result of one dice roll? c) If I had an array that contained the numbers 1 - 100 non-sequentially, and I removed one element from the array, what would be the most computationally efficient way to deduce which element I removed?