The number of crimes that occurred in a certain city per 1000 people had decreased from 46.1 in 1920 to 45.1 in 1970 Find the average rate of change in the number of crimes per 1000 people that occurred from 1920 to 1970.
average rate of change = change in crimes / number of years
average rate of change = ( 46.1 - 45.1 ) / ( 1970 - 1920 ) = 1 / 50 = 0.02