My friend asked me about histograms and sent me some examples given by their teachers and in the textbook. It is not like the histograms that I've learned at all. I was taught that the quantity represented by the area of the bars and the height of the bars represent frequency and are calculated from bar width (for example, I would expect the "number of years" from image 2 to be represented by area of the bars, and not the y axis). Am I missing something? Image one is from a textbook while image two is from a worksheet.

My friend asked me about histograms and sent me some examples given by their teachers and in the textbook. It is not like the histograms that I've learned at all. I was taught that the quantity represented by the area of the bars and the height of the bars represent frequency density and are calculated from bar width (for example, I would expect the "number of years" from image 2 to be represented by area of the bars, and not the y axis). Am I missing something? Image one is from a textbook while image two is from a worksheet.