Final answer:
To find the fraction of cities that have a lake or a river running through them, add the number of cities with lakes and the number of cities with rivers, and divide by the total number of cities.
Step-by-step explanation:
To find the fraction of cities that have a lake or a river running through them, we need to add the number of cities with lakes and the number of cities with rivers, and then divide by the total number of cities.
Given that 3 cities have a lake and 23 cities have a river, the total number of cities with a lake or a river is 3 + 23 = 26.
Therefore, the fraction of cities that have a lake or a river running through them is 26 / 48, which can be simplified to 13 / 24.