 In this video, we provide the solution to question number five for the practice exam number one for math 1050. We're given three graphs and asked to identify which of these three graphs are one to one functions. So the first thing to note here is that to be a one to one function, you have to be a function to determine whether it's a function or not. We run the vertical line test and you'll see that with all three graphs here, there's no problem with vertical lines. Every vertical line hits the graph at most once only on one point. So all of these graphs pass the vertical line test, they are in fact functions that isn't necessary to check here. Now to be a one to one function, it must be a function which additionally passes the horizontal line test. So we're looking for graphs that pass both horizontal and vertical line tests. When you look at graph one, we see that all horizontal lines intersect the graph only a unique point. So this tells us that graph one is in fact a one to one function. Graph two on the other hand, you see that there are horizontal lines that intersect the graph at two different places. That makes it not one to one. In fact, this would tell us the graph is not invertible. So we would exclude two. And then if you look at three right here, same thing, horizontal lines intersect the function only at one point. Therefore three is in fact a one to one function. So the correct answer is going to be one and three, which means we would select choice E.