Convert the fractional part to a decimal.

Since the fourth decimal place is 6 (which is 5 or greater), we round up the third decimal place.

$$8.41666... \approx 8.417$$

The value of $8 \frac{5}{12}$ in 3 decimal places is $\boxed{\text{8.417}}$.

23. Convert 308.5% as a decimal.

$$\frac{308.5}{100} = 3.085$$

308.5% as a decimal is $\boxed{\text{3.085}}$.

24. After 36% of water leaked from our school tank, 960 litres still remained. How many litres of water leaked?

$$\text{Percentage remaining} = 100\% - \text{Percentage leaked}$$ $$\text{Percentage remaining} = 100\% - 36\% = 64\%$$

We know that 960 litres represents 64% of the total capacity. Let $T$ be the total capacity.

$$0.64 \times T = 960$$ $$T = \frac{960}{0.64}$$ $$T = 1500 \text{ litres}$$

$$\text{Leaked water} = \text{Total capacity} - \text{Remaining water}$$ $$\text{Leaked water} = 1500 \text{ litres} - 960 \text{ litres}$$ $$\text{Leaked water} = 540 \text{ litres}$$

Alternatively, calculate 36% of the total capacity:

$$\text{Leaked water} = 36\% \times 1500 \text{ litres}$$ $$\text{Leaked water} = \frac{36}{100} \times 1500$$ $$\text{Leaked water} = 0.36 \times 1500 = 540 \text{ litres}$$

The amount of water that leaked was $\boxed{\text{540 litres}}$.

25. The question "A farmer spent 36,200/- on s during the planting season sh..." is incomplete. Please provide the full question for me to solve it.