Frequency Graphs
1. **State the problem:** We have age groups of employees and their frequencies. We need to draw a frequency polygon, frequency curve, and histogram with frequency polygon on the same graph.
2. **Calculate midpoints for each age group:**
- For 16-20: midpoint $= \frac{16+20}{2} = 18$
- For 21-25: midpoint $= \frac{21+25}{2} = 23$
- For 26-30: midpoint $= \frac{26+30}{2} = 28$
- For 31-35: midpoint $= \frac{31+35}{2} = 33$
- For 36-40: midpoint $= \frac{36+40}{2} = 38$
3. **Frequency data:**
- 16-20: 10
- 21-25: 18
- 26-30: 24
- 31-35: 12
- 36-40: 6
4. **Draw frequency polygon:**
- Plot points at midpoints vs frequency: $(18,10), (23,18), (28,24), (33,12), (38,6)$
- Connect these points with straight lines.
- To close the polygon, add points at the start and end with frequency zero:
- Before 16-20 midpoint: $13$ (midpoint of 11-15) with frequency 0
- After 36-40 midpoint: $43$ (midpoint of 41-45) with frequency 0
- So points for polygon: $(13,0), (18,10), (23,18), (28,24), (33,12), (38,6), (43,0)$
5. **Draw frequency curve:**
- Smooth curve passing through the same points as the frequency polygon.
6. **Draw histogram:**
- Draw bars for each class interval with height equal to frequency.
- Width of each bar corresponds to class width (5 years).
7. **Draw frequency polygon on same graph as histogram:**
- Plot the polygon points on top of histogram bars and connect with lines.
This completes the graphical representation of the data.
Final answer: Frequency polygon points are midpoints with frequencies connected by lines including zero frequency points at start and end.