What this guide covers
Selected Sec 2 S1 measures of centre and grouped-mean skills. Quartiles, box plots and standard deviation are later work.
Count observations, not rows
For a frequency table, total all value×frequency products and divide by the sum of frequencies. For a median, use the middle position(s) in the ordered data. For grouped intervals, use midpoints and say the result is estimated.
Read a frequency table
Values 2, 4 and 6 have frequencies 3, 5 and 2. Find the mean, median and mode.
- There are 3+5+2=10 observations, with total 2(3)+4(5)+6(2)=38. Mean =3810=3.8.
- In the ordered list, positions 5 and 6 are both 4, so median =4.
- The most frequent value is 4 (five occurrences), so mode =4.
Check: The mean 3.8 lies between the smallest and largest observed values, 2 and 6.
Try it yourself
Work on paper, then compare the steps. These checks do not establish mastery.
Find the mean and median of 3, 7, 9 and 11.
Mean =(3+7+9+11)4=304=7.5. The ordered middle pair is 7 and 9, so median =(7+9)2=8.
Ten values are grouped: 0≤x<10 has frequency 4; 10≤x<20 has frequency 6. Estimate the mean and explain why it is not exact.
Use midpoints 5 and 15: estimated mean =[4(5)+6(15)]10=11010=11. Exact positions inside each interval are unknown, so this is an estimate.
Where this connects
- Earlier: read data displays →
Labels and frequencies need careful reading before summarising.
- Later: spread and cumulative frequency →
The Upper Secondary guide adds box plots, quartiles and further comparison.
Sources and scope
Original Mentora data sets aligned to selected Sec 2 S1 content in the MOE G2/G3 Mathematics syllabus. No school table was copied.