Six questions a sheet asking how much taller one bar is than another, and only two charts between them - three questions share each chart, about different pairs of categories. That sharing is the point of the page rather than a saving: comparing two bars means holding both in view at once, which a sheet that redrew the chart for every question would never ask a student to do.
Every bar ends exactly on a labelled gridline, because the values are drawn as multiples of the grid step rather than drawn freely and rounded to look close. So a difference is always read off the chart exactly, and a student who lands between two lines has misread the bar rather than met an awkward number.
Read the value at the top of each bar against the scale on the left, then subtract the smaller from the larger. The answer is how many more the taller category has.
Because that is how the topic is taught. Each chart carries three questions about different pairs of categories, so a student reads one chart carefully instead of glancing at six.
No. Every value is a multiple of the grid step, so each bar ends on a labelled line and can be read exactly.
Reading Bar Graphs asks for one bar's value at a time, and the Bar Graph Worksheets page mixes every question type on one sheet.