A car travels $20\text{km}$ in the first one-fourth part of an hour, $25\text{km}$ in the second one-fourth part, and $15\text{km}$ in the third one-fourth part. What is the average speed of the car (in $\text{km/h}$) during the entire journey?

To find the average speed during the entire journey, we use the formula:
$$\text{Average Speed}=\frac{\text{Total Distance}}{\text{Total Time}}$$

1. Total Distance Travelled:

$$\text{Total Distance}=20\text{km}+25\text{km}+15\text{km}=60\text{km}$$

2. Total Time Taken:
The journey consists of three parts, each lasting for one-fourth of an hour ($\frac{1}{4}$ hour).

$$\text{Total Time}=\frac{1}{4}\text{h}+\frac{1}{4}\text{h}+\frac{1}{4}\text{h}=\frac{3}{4}\text{hour}$$

3. Average Speed:

$$\text{Average Speed}=\frac{60}{\frac{3}{4}}=60\times \frac{4}{3}$$

$$\text{Average Speed}=20\times 4=80\text{km/h}$$

Therefore, the average speed of the car during the entire journey is $80\text{km/h}$.