A standard deck of cards contains 52 cards, with 13 cards in each of the 4 suits: hearts, diamonds, clubs, and spades.
We are asked to find the probability of drawing one heart and one diamond.
Step 1: Find the probability of drawing a heart first and a diamond second.
- The probability of drawing a heart first is:
\[
P(\text{Heart first}) = \frac{13}{52} = \frac{1}{4}
\]
- After drawing the heart, there are now 51 cards left, with 13 diamonds remaining. The probability of drawing a diamond second is:
\[
P(\text{Diamond second}) = \frac{13}{51}
\]
The combined probability of drawing a heart first and a diamond second is:
\[
P(\text{Heart first and Diamond second}) = \frac{1}{4} \times \frac{13}{51} = \frac{13}{204}
\]
Step 2: Consider the reverse case, where a diamond is drawn first and a heart second.
- The probability of drawing a diamond first is:
\[
P(\text{Diamond first}) = \frac{13}{52} = \frac{1}{4}
\]
- After drawing the diamond, there are now 51 cards left, with 13 hearts remaining. The probability of drawing a heart second is:
\[
P(\text{Heart second}) = \frac{13}{51}
\]
The combined probability of drawing a diamond first and a heart second is also:
\[
P(\text{Diamond first and Heart second}) = \frac{1}{4} \times \frac{13}{51} = \frac{13}{204}
\]
Step 3: Add the probabilities of both cases to get the total probability:
\[
P(\text{Heart and Diamond}) = \frac{13}{204} + \frac{13}{204} = \frac{26}{204} = \frac{13}{102} \approx 0.1275
\]
Final Answer:
\[
\boxed{0.13}
\]