Why do the bars on a histogram touch with no gaps?

Because the data is continuous, so the classes are adjacent

A composite (stacked) bar chart is most useful for showing what?

How a total breaks into its parts

11questions. Pick an answer and you'll see why right away.

On a pie chart of $80$ people, $20$ chose cycling. What angle represents cycling?
A class $10 \le t < 30$ has a frequency of $40$ . What is its frequency density?
On a histogram with unequal class widths, what represents the frequency of a class?
For $80$ values, at what cumulative frequency do you read the lower quartile?
A data set has $Q_1 = 25$ and $Q_3 = 45$ . What is the interquartile range?
Which diagram keeps the original data values while showing the shape of the data?
Why do the bars on a histogram touch with no gaps?
A histogram bar has frequency density $5$ over a class width of $4$ . What is its frequency?
On a cumulative frequency graph, against what should cumulative frequency be plotted?
A composite (stacked) bar chart is most useful for showing what?
A data set has $Q_1 = 30$ and $Q_3 = 50$ . Using the $1.5 \times \text{IQR}$ rule, what is the upper boundary for outliers?