Mdu has made both cities richer because the average salary has gone up in both due to his move. Can you explain how that could happen?
Describe what is needed for one person moving to:
a) increase the average income in both cities
b) decrease the average income in both cities or
c) increase one whilst decreasing the other.
In what circumstances could Mdu, moving from one place to another, reduce the average income in one place and double the average income in the other?
See www.nrich.maths.org/6400 and Notes for Teachers – For Richer for Poorer