The probability of rain tomorrow is $\frac{3}{10}$.  What is the probability that it will not rain tomorrow?  Express your answer as a common fraction.
I know that the sum of the probabilities of all possible outcomes of an event is 1. So, if the probability of rain tomorrow is $\frac{3}{10}$, then the probability of no rain tomorrow is 1 minus $\frac{3}{10}$. I can subtract fractions by finding a common denominator and then subtracting the numerators. The common denominator of 1 and $\frac{3}{10}$ is 10, so I can write 1 as $\frac{10}{10}$. Then, $\frac{10}{10} - \frac{3}{10} = \frac{7}{10}$. So, the probability that it will not rain tomorrow is $\frac{7}{10}$. 