Each value with how often it occurs: A frequency table lists each data value (or class) with its frequency — how many times it occurs.
Add a column of frequencies to get the total; the mode is the value with the highest frequency.
A histogram groups data into equal class intervals; bar heights are the frequencies (bars touch). The tallest bar is the modal class.
Interactive diagram
Explore the labelled diagram, charts and maps for this topic in full study mode.
IB-style question — read the table
A survey of 40 households records the number of pets owned: 0 pets → 9 households, 1 → 15, 2 → 11, 3 → 5.
Find the mode and the number of households with at least 2 pets.
Step by step
- Mode = the value with the highest frequency.
- 'At least 2' means 2 or 3.
Final answer
Mode = 1 pet; 16 households own at least 2 pets.
Mode = most frequent VALUE: The mode is the data value, not its frequency — here the mode is 1, not 15.
Free preview
This is the free notes preview
You're reading the free notes. Aimnova Pro unlocks the full study experience — and you can try it with your first topic free to keep:
- FlashcardsLock in vocabulary and key terms with spaced repetition.
- Practice questionsAnswer exam-style questions and get instant AI marking.
- Mock exams & past-paper vaultSit full mocks and see exactly how examiners award marks.
- Personalised study planA daily plan built around your exam date and weak areas.
Bars for grouped continuous data: A histogram shows grouped continuous data.
With equal-width classes the bar height is the frequency, and the bars touch (no gaps).
Add the heights to get the total.
IB-style question — read a histogram
A histogram of parcel masses uses equal 2 kg classes with frequencies 6, 14, 18, 9, 3.
Find the total number of parcels and how many weigh under 4 kg.
Step by step
- Total = sum of all the bar heights.
- 'Under 4 kg' = first two classes.
Final answer
50 parcels in total; 20 weigh under 4 kg.
Continuous data → bars touch: Histograms are for continuous data, so the bars touch.
Bar charts (gaps between bars) are for categories — don't confuse them.
Memorize terms 3x faster
Smart flashcards show you cards right before you forget them. Perfect for definitions and key concepts.
The tallest bar's class: For grouped data the modal class is the class with the greatest frequency (the tallest bar).
You can also describe the shape: roughly symmetric, or skewed toward higher/lower values.
IB-style question — modal class
Heights (cm) are grouped: 150–160 → 5, 160–170 → 12, 170–180 → 9, 180–190 → 4.
State the modal class and describe the distribution.
Step by step
- Modal class = the class with the highest frequency.
- Compare the tails.
Final answer
Modal class 160 ≤ h < 170 cm; the distribution rises to that class then falls away (roughly symmetric).
Modal class ≠ a single mode: For grouped data you can only name the modal class (an interval), not a single modal value.