Two boats, travelling at $5$ and $10$ kms per hour, head directly towards each other. They begin at a distance of $20$ kms from each other. How far apart are they (in kms) one minute before they collide?

The boats together travel 10 + 5 = 15 km in 60 minutes.

In one minute they can travel=$\frac{60}{15}=\frac{1}{4}$km

They are $\frac{1}{4}$ km apart,one minute they collide

Hence,Option (3)$\frac{1}{4}$ is the correct choice.