Grouping data into classes, class limits, boundaries, midpoints and width, histograms with equal bars, frequency polygons, and estimating the mean, modal class and median class.
5 narrated scenes. Press play, listen and read along — the points appear as they are explained. Use ‹ Prev / Next › or the scene bar to jump to any scene.
When there are 200 different heights, a list is useless. Group them into classes and a pattern appears at once — and you can still estimate the mean.
Narration uses your device’s built-in voice. No sound? Switch to “Captions only” — the captions advance on their own.
Copy these into your notebook in your own words — that is how they stick.
The stated ends of a class, e.g. 140–149.
Halfway between the upper limit of one class and the lower limit of the next: 139.5 and 149.5.
Width = upper boundary − lower boundary. Midpoint = (lower limit + upper limit) ÷ 2.
Equal widths: bars touch, drawn between boundaries, height = frequency.
Plot (midpoint, frequency); join with straight lines; close at both ends with f = 0.
Σfx ÷ Σf with x = class midpoint.
Highest frequency.
Class that contains the (n/2)-th value (use cumulative frequency).
3 quick games on this lesson. Earn XP and badges as you play — your best score for each game is saved. Games are for practice and do not change your exam readiness. More games in the Mathematics Arcade.
8 items modelled on real CSEC Paper 1 questions. Choose one answer for each, then check. Aim for 80% or better. Work each item on paper first.
Write full answers, then reveal the mark scheme and tick the points you earned (20 marks in total). Show all your working — method marks count. Your answers are saved on this device.
Question 1 [11 marks]
The heights of 40 students are summarised in the table: 140–149 (6), 150–159 (10), 160–169 (14), 170–179 (7), 180–189 (3).
(a) State (i) the class boundaries and the class width of the third class, and (ii) its midpoint. [3]
(b) Calculate an estimate of the mean height, to 2 decimal places. [4]
(c) State the modal class and the class containing the median. [2]
(d) Estimate the percentage of students taller than 169.5 cm. [2]
Question 2 [9 marks]
Use the grouped data in the table above.
(a) On graph paper draw a histogram of the data. (Check: boundaries on the x-axis from 139.5 to 189.5, bars touching, heights 6, 10, 14, 7, 3, labelled axes with units, title.) [4]
(b) On the same graph or a new one, draw the frequency polygon. State which values you plot. [3]
(c) Explain why the mean calculated from grouped data is only an estimate. [2]
Find these in your own past-paper booklets for extra timed practice. Items above are written in the style of these papers; any adapted from a specific question say so.