Okay, here we have this:
Considering the provided information and probability, we are going to calculate the requested probability, so we obtain the following:
So let's remember that the probability of an event plus its complement is equal to 1, therefore we have:
Probability of snow falling+Probability of not snowing=1
Probability of not snowing=1-Probability of snow falling
Probability of not snowing=1-(7/10)
Probability of not snowing=(10/10)-(7/10)
Probability of not snowing=(10-7)/10
Probability of not snowing=3/10
Finally we obtain that the correct answer is the option B.
