Question:
The probability that it will rain tomorrow is 0.85. What is the probability that it will not rain tomorrow?
Solution:
Let $A$ be the event of raining tomorrow.
The probability that it will rain tomorrow, $\mathrm{P}(\mathrm{A})$, is $0.85$.
Since the event of raining tomorrow and not raining tomorrow are complementary to each other, the probability of not raining tomorrow is:
$\mathrm{P}(\overline{\mathrm{A}})=1-\mathrm{P}(\mathrm{A})=1-0.85=0.15$