Derek is watching the construction cranes downtown and is trying to figure out how much taller they have to be than the building they are building. He sees one crane that is 228 feet tall finishing a building that was 200 feet tall. He sees another that is 120 feet tall finishing a building that is 100 feet tall. The final crane he sees is 147 feet tall, finishing a building that is 140 feet tall. On average, what percentage taller are the cranes than the building? Let's be accurate as possible.
The first crane is 14 percent taller because if 200 + 200x = 228 then x = .14. The second crane is 20 percent taller because if 100 + 100x = 120 then x = .2. The third crane is 5 percent taller because if 140 + 140x = 147 then x = .5. The total percent is 39 because 14 + 20 + 5 = 39. The average percent greater the height of the crane is than the building is 13 because 39 / 3 = 13.
The answer: 13.