GCSE Maths Unit 1 - Boxplots Guide
March 29, 2016
GCSE Maths: Boxplots
What do boxplots express?
Every boxplot gives a minimum, lower quartile, median, upper quartile and maximum as shown in the diagram below.
Range = Highest value – Lowest value
Interquartile Range = upper quartile – lower quartile
A small interquartile range shows the data is quite consistent while a large interquartile range shows that the data is quite inconsistent
Girls and boys are timed in a race and the box plot gives information about the girls’ times.
The following information is known about the boys’ times:
(1) 25% of the boys take 12 seconds or less
(2) The interquartile range for the boys is the same as for the girls
(3) The ratio of median times is girls : boys = 8:7
(4) The time of the fastest boy is 10.5 and the time of the slowest boy is 18.5.
Complete a box plot for the boys’ times.
Lower quartile = 12 seconds
Interquartile range for the girls = 4 = Interquartile range for the boys
Upper quartile = 12 + 4 = 16
Boys’ median = 7/8 x girls’ median = 7/8 x 16 = 14
Fastest and slowest times are 10.5 and 18.5 seconds respectively