Drawing Histograms Flashcards

All 7 cards in this deck

What are the steps to draw a histogram from a grouped frequency table?

e.g. $0 < t \le 10$ has frequency $20$

1. Find each class width: $10 - 0 = 10$
2. Frequency $\div$ class width $=$ frequency density: $20 \div 10 = 2$
3. Draw a bar from $0$ to $10$ of height $2$, axis labelled 'frequency density', with no gaps between bars.

What must the vertical axis of a histogram be labelled?

Frequency density.

In a histogram, what does the width of each bar represent?

The class interval, drawn from its lower bound to its upper bound.

How do you find the height of a missing bar when completing a histogram?

e.g. the class $40 < t \le 60$ has frequency $24$

Divide the frequency by the class width to get the frequency density.

e.g. $24 \div 20 = 1.2$

True or false? A histogram is drawn with gaps between the bars.

False. The data is continuous, so the bars touch each other.

True or false? All the bars of a histogram must be the same width.

False. Unequal class intervals give bars of different widths; the frequency density scale keeps the areas correct.

True or false? If all the class intervals in a histogram have the same width, the heights of the bars are proportional to the frequencies.

True. Each frequency is divided by the same class width, so the frequency densities are in the same proportion as the frequencies.