Continuous data (Chapter 17) 355Height (mm) Frequency
206 h< 40 4
406 h< 60 17
606 h< 80 15
806 h< 100 8
1006 h< 120 2
1206 h< 140 42 A plant inspector takes a random sample of ten week old plants from
a nursery and measures their height in millimetres.
The results are shown in the table alongside.
a What is the modal class?
b Estimate the mean height.
c How many of the seedlings are 40 mm or more?
d What percentage of the seedlings are between 60 and 80 mm?
e If the total number of seedlings in the nursery is 857 , estimate
the number which measure:
i less than 100 mm ii between 40 and 100 mm.06 d< 1 16 d< 2 26 d< 3 36 d< 4 46 d< 5
Number of students 76 87 54 23 5Time (t) 56 t< 10 106 t< 15 156 t< 20 206 t< 25 256 t< 30 306 t< 35
Frequency 2 8 16 20 24 10When data is recorded for a continuous variable there are likely to be many different values. This data is
therefore organised usingclass intervals. A special type of graph called ahistogramis used to display the
data.A histogram is similar to a bar chart but, to account for the continuous nature of the variable, the bars are
joined together.B HISTOGRAMS [11.6]
discrete data continuous dataColumn Graph Histogram3 The distances travelled to school by a random sample of students were:a What is the modal class?
b Estimate the mean distance travelled by the students.
c What percentage of the students travelled at least 2 km to school?
d If there are 28 students in Josef’s class, estimate the number who travelled less than 1 km to school.4
a What percentage of the players finished the game in less than 20 minutes?
b Estimate the mean time to finish the game.
c If 2589 other people play the game, estimate the number who will complete it in less than 25
minutes.The times taken in minutes for players to finish a computer game were:Distance ( m)kIGCSE01
cyan magenta yellow black(^05255075950525507595)
100 100
(^05255075950525507595)
100 100
Y:\HAESE\IGCSE01\IG01_17\355IGCSE01_17.CDR Tuesday, 18 November 2008 11:47:22 AM PETER