What type of chart is this — a stacked bar chart or a 100% stacked bar chart?
Answer: Both. Each piece is an amount of time (a stacked bar), and every column has the same total, 24 hours, so the pieces are also the shares of the day (a 100% stacked bar).
Step-by-step solution
Idea: A 100% stacked bar makes all totals equal artificially. When the totals are really equal (every day has 24 hours), the stacked chart and the 100% chart look exactly the same.
- It is a stacked bar chart because each small piece shows an amount of time (in hours, on the right-hand scale) spent on an activity, and the pieces add up to the total.1 mark
- It is also a 100% stacked bar chart because every column’s total is the same, 24 hours, so the lengths of the pieces within and across the columns also show the proportions of the day (left-hand scale). With equal totals, the two charts coincide.1 mark
It is both: a stacked bar chart (pieces are hours spent) and a 100% stacked bar chart (every column totals 24 hours, so the pieces are also shares of the day).
Answer to write in the exam
Each piece = time spent on an activity ⇒ stacked bar chart
Every column total = 24 h ⇒ lengths also show shares ⇒ 100% stacked bar chart
∴ The chart is both
Common mistakes that cost marks
- Choosing only one type. Because all totals are 24 hours, it is both.
- Thinking any stacked chart with equal-looking bars is a 100% chart; the totals must truly be equal.
- Forgetting that a single stacked bar can always be read as a 100% bar too.
How this can come in the exam
MCQ (1 mark)
A stacked bar chart can also be read as a 100% stacked bar chart when
- all bars have different totals
- all bars have the same total
- each bar has only two pieces
- the bars are vertical
Show answer
(B) all bars have the same total
With equal totals, piece lengths show both amounts and shares.
Try one yourself
Three classes each have 40 students; a stacked bar shows how many walk, cycle or take the bus. Is this also a 100% stacked bar chart?
Show answer
Yes. All totals are 40, so each piece’s length also shows its share; e.g. 10 walkers = 25%.
More questions like this
- Do you remember the ‘What Can A Strip Say?’ activity from last year? In each strip, if we club the tiny strips belonging to each activity together, will we get a 100% stacked bar chart like the one in the figure?
- The smart watch data of 5 people was tracked from Monday to Friday. The recorded data tells us how many hours each person spent lying down, sitting, and standing or moving around, etc., as shown in the following table.
- 1. Will the bars look similar if a different teacher’s data is considered instead of Zakir’s?
2. Will the bars look different if the data for all 7 days of the week is considered?
3. Some bars in the chart may also match people doing other kinds of work/activities. Can you think of any? Discuss. - In cricket, the run rate is the average number of runs scored per over. In a T20 match, a team scored 6 runs in the first over making the run rate 6.
- Five friends who play badminton surveyed the city and collected the price of shuttlecocks across brands and types (Nylon and Feather). The following is the list of the prices, in rupees (₹), that each one compiled.
Yusuf: 40(N), 105(N), 383(F), 108(N), 165(F), 116(F)
Srikanth: 194(N), 85(N), 93(N), 121(N)
Kashvi: 49(N), 297(F), 105(N), 275(F), 40(N)
Prasanna: 124(N), 333(F), 182(N), 258(F)
Gracy: 220(F), 458(F), 129(F), 183(N)
Can you describe a way they can work together to find the average price of a shuttlecock across types?