Yang Gao: 1) Describe briefly the concept of differential privacy. Differential privacy arises because absolute guarantees about privacy is not possible (the example of Terry Gross’s height), thus it’s necessary to change to a relative one: the presenting or not presenting of any individual could not make much difference to the answer of the questions based on the perturbed database. This is also true for a small group of people who concerns their privacy when they appear in the database as a whole. However, differential privacy does not guarantee anything about larger group’s privacy, which is their main relaxation. 2) Which query result will have more noise: the average of all the salaries in the database or retrieving Bob's salary? The latter one. Because the sensitivity of the latter function is very large. (see def. 3 in the paper.)