Flashcards · 4040 · Topic 4

Formation of frequency distributions into cumulative frequency distributions flashcards

9 cards on Topic 4, subtopics 4.1 to 4.2. Pick a subtopic or study them all.

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What does a cumulative frequency of 33 at x = 3 mean?: 33 observations are less than or equal to 3. Cumulative frequency is the running total of the frequencies.
How do you build a cumulative frequency table for grouped data?: Add each frequency to the running total and label each total with the upper class boundary. The last total must equal the total frequency.
Cumulative frequencies at the ends of four classes are 3, 10, 24 and 30. Find the class frequencies: Subtract each cumulative frequency from the next: 3, 7, 14, 6. The first class keeps its value.
What can you read from a cumulative frequency table without drawing a graph?: At a class boundary only: items up to it (read directly), between two boundaries (subtract), above it (total − cumulative frequency). Values between boundaries must be estimated.

Where do you plot the points of a cumulative frequency graph?: At the upper class boundaries, starting with cumulative frequency 0 at the lower boundary of the first class.
What is the difference between a cumulative frequency polygon and a curve?: A polygon joins the plotted points with straight lines; a curve joins them with one smooth curve. Read the question to see which is wanted. Both give estimates.
How do you read a cumulative frequency graph in each direction?: From a value: go up from the horizontal axis to the graph, then across, to read the number of items at most that value. From a number of items: go across from the vertical axis, then down, to read a value.
How do you answer "more than" and "the highest k items" questions from a cumulative graph?: "More than" a value: total − the reading at that value. "Highest k items": read across at cumulative frequency total − k.
Lengths measured to the nearest mm are grouped 30–39, 40–49, … Where does the graph start?: At (29.5, 0). 29.5 is the true lower boundary; 30 is only the class limit.