A bowl contains seven blue chips and three red chips. Two chips are to be drawn successively at random and without replacement. We want to compute the probability that the first draw results in a red chip $(A)$ and the second draw results in a blue chip $(B)$. 
It is reasonable to assign the following probabilities:
$$
P(A)=\frac{3}{10} \text { and } P(B \mid A)=\frac{7}{9} \text {. }
$$
The probability of obtaining red on the first draw and blue on the second draw is
$$
P(A \cap B)=\frac{3}{10} \cdot \frac{7}{9}=\frac{7}{30}
$$