**Step 1 — Prepare the cumulative frequency table.**

| Age (yrs) | $f_i$ | Cumulative frequency (cf) |
|---|---|---|
| 15 – 20 | 2 | 2 |
| 20 – 25 | 4 | 6 |
| 25 – 30 | 18 | 24 |
| 30 – 35 | 21 | 45 |
| **35 – 40** | **33** | **78** |
| 40 – 45 | 11 | 89 |
| 45 – 50 | 3 | 92 |
| 50 – 55 | 6 | 98 |
| 55 – 60 | 2 | 100 |
| **Total** | **100** | |

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### MODAL AGE

**Step 2 — Identify the modal class.**
The highest frequency is $33$, so the modal class is **35 – 40**.
$$l = 35,\quad f_1 = 33,\quad f_0 = 21,\quad f_2 = 11,\quad h = 5$$

**Step 3 — Apply the mode formula.**
$$\text{Mode} = l + \left(\frac{f_1 - f_0}{2f_1 - f_0 - f_2}\right) \times h$$

**Step 4 — Substitute.**
$$= 35 + \left(\frac{33 - 21}{66 - 21 - 11}\right) \times 5 = 35 + \left(\frac{12}{34}\right) \times 5$$

**Step 5 — Calculate.**
$$= 35 + \frac{60}{34} = 35 + 1{\cdot}76 = 36{\cdot}76 \text{ years}$$

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### MEDIAN AGE

**Step 6 — Locate the median class.**
$$\frac{N}{2} = \frac{100}{2} = 50$$
The cumulative frequency just greater than 50 is 78, so the median class is **35 – 40**.
$$l = 35,\quad cf = 45,\quad f = 33,\quad h = 5$$

**Step 7 — Apply the median formula.**
$$\text{Median} = l + \left(\frac{\frac{N}{2} - cf}{f}\right) \times h$$

**Step 8 — Substitute.**
$$= 35 + \left(\frac{50 - 45}{33}\right) \times 5 = 35 + \frac{25}{33}$$

**Step 9 — Calculate.**
$$= 35 + 0{\cdot}76 = 35{\cdot}76 \text{ years}$$

$$\boxed{\text{Modal age} \approx 36{\cdot}76 \text{ years}, \qquad \text{Median age} \approx 35{\cdot}76 \text{ years}}$$