Answer:
After the 8th city is built there will be 28 roads between the cities
Explanation:
The given parameters are;
The number of cities initially on the island = 7 cities
The number of roads between each 2 cities = 1 road
Therefore, we have the number of roads between the 7 cities are;
7 cities taking 2 at a time = ₇C₂
The initial number of roads between the 7 cities = 21 roads
The number of roads, 'n' there will be after the 8th city is built is therefore;
The number of roads there will be after the 8th city is built, n = 28 roads.