Michelle draws a card from a standard deck of 52 cards. She replaces the card and draws a second card. What is the probability that she draws a heart and then a spade?
[Note: There are 13 each of hearts, spades, clubs, and diamonds.]
Since Michelle replaces the first card before drawing the second card, the probability of drawing a heart and then a spade is the product of the probabilities of drawing a heart on the first draw and a spade on the second draw.
There are 13 hearts in a deck of 52 cards, so the probability of drawing a heart on the first draw is $\dfrac{13}{52}=\dfrac{1}{4}$.
Similarly, there are 13 spades in a deck of 52 cards, so the probability of drawing a spade on the second draw is $\dfrac{13}{52}=\dfrac{1}{4}$.
Therefore, the probability of drawing a heart and then a spade is $\dfrac{1}{4}\times\dfrac{1}{4}=\boxed{\dfrac{1}{16}}$.