We have seen that the daily number of phone calls between two cities varies jointly as
Chapter 6, Problem 51(choose chapter or problem)
We have seen that the daily number of phone calls between two cities varies jointly as their populations and inversely as the square of the distance between them. This model, used by telecommunication companies to estimate the line capacities needed among various cities, is called the gravity model. Compare the model to Newtons formula for gravitation on page 486 and describe why the name gravity model is appropriate.
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