Mean And Mode
1. **State the problem:** We have grouped data of student ages and their frequencies. We need to calculate the mean age and analyze the histogram to find the modal age.
2. **Calculate the mean age:**
- Intervals and frequencies are:
- 18-<19: 24 students
- 19-<20: 70 students
- 20-<24: 76 students
- 24-<26: 48 students
- 26-<30: 16 students
- 30-<32: 6 students
- Find midpoints of each age group:
- 18-<19 midpoint = $\frac{18 + 19}{2} = 18.5$
- 19-<20 midpoint = $\frac{19 + 20}{2} = 19.5$
- 20-<24 midpoint = $\frac{20 + 24}{2} = 22$
- 24-<26 midpoint = $\frac{24 + 26}{2} = 25$
- 26-<30 midpoint = $\frac{26 + 30}{2} = 28$
- 30-<32 midpoint = $\frac{30 + 32}{2} = 31$
- Calculate sum of $\text{midpoint} \times \text{frequency}$:
$$(18.5)(24) + (19.5)(70) + (22)(76) + (25)(48) + (28)(16) + (31)(6)$$
$$= 444 + 1365 + 1672 + 1200 + 448 + 186 = 5315$$
- Total number of students:
$$24 + 70 + 76 + 48 + 16 + 6 = 240$$
- Mean age $= \frac{5315}{240} = 22.15$ years (approx)
3. **Draw a histogram:** (b)(i)
- Horizontal axis: Age groups 18-<19, 19-<20, 20-<24, 24-<26, 26-<30, 30-<32
- Vertical axis: Number of students as bar heights
- Bars heights: 24, 70, 76, 48, 16, 6 respectively
4. **Estimate the modal age from histogram:** (b)(ii)
- The tallest bar corresponds to age group 20-<24 with 76 students.
- Mode is estimated as the midpoint of this group: $22$ years approximately.
**Final answers:**
- Mean age $\approx 22.15$ years
- Estimated modal age $\approx 22$ years