It rains 40%

According to the meaning of the question, it rains exactly two days out of three days. The following 20 groups of random numbers are generated by random simulation.

Among the 20 groups of random numbers, there are 19 1, 27 1, 932,812,393, 137.

***6 groups of random numbers,

The probability of seeking is 7 20.

So the answer is: 7 20.