In a certain city, it is always either sunny or rainy. If it's sunny on Monday, there's a 1/3 chance it will be sunny on Tuesday. If it's rainy on Monday, there's a 2/3 chance it will be sunny on Tuesday. Given that it was sunny on Sunday, what is the probability that it will be sunny on both Monday and Tuesday?
The probability of it being sunny on both Monday and Tuesday is 4/9.

Here's the reasoning behind this:

1. We are given that it was sunny on Sunday.
2. Let A be the event "it is sunny on Monday" and B be the event "it is sunny on Tuesday."
3. We want to find the probability P(A ∩ B), which means the probability of both events A and B occurring.
4. To do this, we can use the conditional probability formula:
   P(A ∩ B) = P(B|A) * P(A)
5. We know that if it's sunny on Monday (event A), there's a 1/3 chance it will be sunny on Tuesday (P(B|A) = 1/3).
6. Since it's either sunny or rainy in the city, and it was sunny on Sunday, we assume an equal chance for it to be sunny or rainy on Monday. So, P(A) = 1/2.
7. Now, we can calculate P(A ∩ B):
   P(A ∩ B) = (1/3) * (1/2) = 1/6
8. However, we also need to consider the case where it's rainy on Monday but still sunny on Tuesday. Let C be the event "it is rainy on Monday." Then, P(C) = 1/2 and P(B|C) = 2/3.
9. We can calculate the probability of it being sunny on Tuesday given that it was rainy on Monday:
   P(B ∩ C) = P(B|C) * P(C) = (2/3) * (1/2) = 1/3
10. Finally, we need to find the total probability of it being sunny on both Monday and Tuesday by adding the probabilities from steps 7 and 9:
    Total probability = P(A ∩ B) + P(B ∩ C) = 1/6 + 1/3 = 3/6 + 2/6 = 4/9