Drawing an ogive, reading the median and quartiles, the interquartile range, percentages above or below a value, comparing distributions and making inferences.
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.
“Half the students are shorter than what height?” “What percentage ran faster than 14 seconds?” A cumulative frequency curve answers every question of this kind with a ruler.
Narration uses your device’s built-in voice. No sound? Switch to “Captions only” — the captions advance on their own.
Read the median and quartiles from the curve.
Copy these into your notebook in your own words — that is how they stick.
Running total of frequencies; last value = total.
Plot (upper class boundary, cumulative frequency); smooth curve from the lower boundary of the first class.
Read at cf = n/2.
Q₁ at n/4, Q₃ at 3n/4; IQR = Q₃ − Q₁; semi-IQR = IQR ÷ 2.
Upper boundary of the last class − lower boundary of the first class.
Read cf at the value; above = n − cf; × 100 ÷ n.
Average (median) and spread (IQR / standard deviation).
State the evidence (numbers), the comparison, and any limits.
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 (21 marks in total). Show all your working — method marks count. Your answers are saved on this device.
Question 1 [14 marks]
The times, in minutes, taken by 60 students to complete a quiz are: 0 < t ≤ 10 (4), 10 < t ≤ 20 (11), 20 < t ≤ 30 (20), 30 < t ≤ 40 (16), 40 < t ≤ 50 (9).
(a) Complete a cumulative frequency table. [2]
(b) On graph paper draw the cumulative frequency curve, using 2 cm to 10 minutes on the horizontal axis and 2 cm to 10 students on the vertical axis. (Check: points (10, 4), (20, 15), (30, 35), (40, 51), (50, 60) with (0, 0); smooth curve.) [4]
(c) Use your graph to estimate (i) the median, (ii) the lower and upper quartiles, (iii) the interquartile range. [5]
(d) Estimate the percentage of students who took more than 35 minutes. [3]
Question 2 [7 marks]
Class A: median 62, interquartile range 10. Class B: median 62, interquartile range 24.
(a) Compare the performance of the two classes. [3]
(b) State which class has the larger standard deviation and explain what this means. [2]
(c) Give TWO things to consider before concluding that Class A was taught better. [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.