Final answer:
A city can generate 650 unique two-letter codes for neighborhoods using uppercase alphabets with the restriction that the two alphabets cannot be the same.
Step-by-step explanation:
To calculate how many codes a city can generate for each neighborhood using two uppercase alphabets with the restriction that two alphabets cannot be the same, we use the permutation principle. For the first position of the code, there are 26 possibilities, as there are 26 uppercase letters in the English alphabet. Since the second letter must be different, there will be one fewer choice for the second position, so there are 25 possibilities for the second position.
The total number of unique two-letter codes is found by multiplying the number of possibilities for the first position by the number of possibilities for the second position:
26 (first letter choices) × 25 (second letter choices) = 650 possible codes.