Reading the vertical data in a frequency histogram polygon

[Vital]

Hello.

Please, take a look at the screenshot from the textbook. They say in the textbook that there are in total 48 data observations, 20 of which lie in the interval 0 - 2, and 6 lie in the interval 2 - 4. Yes, both 20 and 6 are more or less clear on the graph, but how did they come up with 48 in total? I simply can't find the correct number on the vertical axis:
- is it 11 (at midpoint -1%) in the interval from -2 to 0?
- is it 8 or 7 (at midpoint -3%) in the interval from -4 to -2?
- is it 3 in the interval from -4 to -2?

How to correctly determine the number on the vertical axis?
Thank you very much!

 

[kuruman]

How to correctly determine the number on the vertical axis?

Draw parallel lines to the x-axis at the points where there is a slope change and see where they intersect the y-axis. The points of intersection must be integers. You should be able to find the closest integer to one of the five subdivisions between adjacent tick marks. Just eyeballing it I get 3, 8, 11, 20, 6 the sum of which is 48.

 

[berkeman]

Just eyeballing it

LOL

 

[kuruman]

LOL

The visual pun was unintentional, thanks for pointing it out.

 

[berkeman]

The visual pun was unintentional, thanks for pointing it out.

Well, it's completely non-obvious. Very subtle. Not many people would notice it. I swear.

 

[Vital]

Draw parallel lines to the x-axis at the points where there is a slope change and see where they intersect the y-axis. The points of intersection must be integers. You should be able to find the closest integer to one of the five subdivisions between adjacent tick marks. Just eyeballing it I get 3, 8, 11, 20, 6 the sum of which is 48.

I see. Thank you very much.