Problem: Pick the corresponding probability histogram.

Process: The x-axis represents the possible inputs of the probability mass function. The y-axis represents the output of the probability mass function given an input from the x-axis. Every vertical bar in an accurate histogram will have its top edge at the y-value corresponding to the value the probability mass function would give if the x-value below the vertical bar was passed to it.

Answer:

Problem: What is the probability that at least two students show up? More than two students show up?

Process: The probability that at least two students show up is equal to , or the sum of all probabilities for values of which are greater than or equal to 2. The probability that more than two students show up is equal to , or the sum of all probabilities of which are greater than 2.
Answer: 0.60 and 0.50.

Problem: What is the probability that between one and three students, inclusive, show up?

Process: ...
Answer: 0.45.