Problem 1:
We have 2 outcomes for each toss, so in all there are 2^3=8 outcomes. There is only one outcome in which we don't get tails at least once, the outcome where we have heads, heads, heads. So, in 7/8 outcomes we get tails at least once.

Problem 2:
Since we're dealing with 1/4 and 1/3, let's pick 12 to represent the number of people interviewed since it is a nice round number. Out of those people, 1/4 said yes to question 1. So, 3 people said yes. Out of those, 1/3 said yes to question 2. So, 1 person said yes to both question 1 and question 2. Since there were 12 people total, 11/12 did not say yes to both questions.