Answer: The required unit rate is 20 milliliters per minute.
Step-by-step explanation: Given that during a thunderstorm yesterday, 600 millimeters of rain fell in 30 minutes.
We are to find the unit rate for millimeter per minute.
We will be using the UNITARY method to solve the problem.
We have
In 30 minutes, rain fell = 600 milliliters.
So, in 1 minute, rain fell is given by

Thus, the required unit rate is 20 milliliters per minute.