Probability questions - an easy one and a hard one:

Question

Question #1: If 2 letters are written and the corresponding envelopes addressed, and the letters are then fitted at random into the envelopes, the probability that both letters will go into wrong envelopes is ____?

Question #2: If 13 letters are written and the corresponding envelopes addressed, and the letters are then fitted at random into the envelopes, the probability that the 13 letters will go into wrong envelopes is ____?

Answer 1

Question #1 => {1/2}×{1/2} = 0.25. ie., 25% chance of that happening.
Question #2 => {12/13}×{12/13}×..... (11 more times) ={12/13}^13 = 0.3532
ie., 35.32% of that happening.