Can a histogram have just one value as its bin in a probability histogram? On [this link], (http://www.henry.k12.ga.us/ugh/apstat/chapternotes/7supplement.html) there is a histogram where on the x-axis, all the sums of the two dice are there {2, 3, 4, 5, ... 12}, and on the y-axis, the probability that they will occur is there.
I thought histograms have to contain a range as their bin. Can someone help me understand this?

As the other answer here points out, it is possible to have a histogram where each bin is a single point (e.g., if we have a "natural" finite number of bins).  I will just supplement the other answer here by noting that in this case we usually would not call this a histogram at all (even though technically it is one).  Usually we would just refer to this as a barplot of the probability mass function.
