Approximately what is the minimum amount of caffeine, in milligrams, consumed per day by a person who daily drinks two 10-ounce mugs of percolated coffee and one 12-ounce cup of a caffeinated soft drink?
The answer is given:
According to the bar graph, the minimum amount of caffeine in a 5-ounce cup of percolated coffee is approximately 40 milligrams. Therefore, the minimum amount of caffeine in two 10-ounce cups of percolated coffee, which is the same as the minimum amount of caffeine in four 5-ounce cups, is approximately (40)(4), or 160 milligrams. The minimum amount of caffeine in a 12-ounce caffeinated soft drink is approximately 30 milligrams. So, the minimum amount of caffeine in two 10-ounce mugs of percolated coffee and one 12-ounce caffeinated soft drink is approximately 160 + 30, or 190 milligrams.
How they have got the percolated coffee approximately 40 milligrams? May be i am confused with the ounce measuring.
They simply read the left endpoint of the bar and see it's a bit below $50$ so they name it $40$
With pixel by pixel zooming you can see that the exact reading would be $\frac{1125}{29}\approx38.7...$ but for these purposes the $1.3$ error dosen't really make any difference.
I think the reason that you posted this is when you look at the graph, it actually dosen't look like it goes down to $40$ but this is all visual things.