The probability that it will not rain tomorrow is the complement of the probability that it will rain.

Given that the probability of rain is 0.85, the probability of no rain (denoted as $P(\text{no rain})$) is calculated as:

$P(\text{no rain}) = 1 - P(\text{rain}) = 1 - 0.85 = 0.15$

So, the probability that it will not rain tomorrow is 0.15.

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Would you like more details on how complementary probabilities work? Let me know if you have any further questions!

Here are 5 related questions:

1. What is the concept of complementary events in probability?
2. How do you calculate the probability of independent events happening together?
3. What is the difference between conditional probability and complementary probability?
4. If the probability of event A is 0.4, what is the probability of event A not occurring?
5. How does the law of total probability apply to situations like weather forecasting?

Tip: When calculating probabilities, remember that the total probability of all possible outcomes always sums to 1.