Teacher's Guide - Pearson

20re t p a h cMeasures of centraltendency and dispersionSyllabus: General objectiveThis chapter deals with knowledge on measures of central tendency and measures ofdispersion.Specific objectives• Find the modal class, median class, and mean class from a frequency tablecomprising of grouped data.• Find modal class and mean class from a histogram comprising of grouped data.• Calculate range and inter-quartile range from a distribution and cumulativefrequency curve.• Estimate quartiles and percentiles from a cumulative frequency curve.AnswersExercise 20.1 (Student’s Book page 367)1. a) i) Modal class is 61–70.ii) Median class is 61–70.iii) Percentage mark Frequency Middle value Middle value 3 frequency31–40 3 35.5 106.541–50 4 45.5 18251–60 16 55.5 88861–70 26 65.5 1 70371–80 14 75.5 1 05781–90 8 85.5 68491–100 9 95.5 859.5Total 80 5 480Mean 5 _____ 5 480​80 ​ 5 68.5So the mean class is 61–70.b) 16 1 26 1 14 1 8 1 9 5 73 students2. a) i) 138–142ii) 138–142126EXPLORING MATHEMATICS FORM 3