(Here is a problem from a math book published in 1900, there titled The New Higher Arithmetic, thumb by A. W. Rich.)

A dealer has land valued at $40, $60, $72, and $80 per acre. How many acres must he sell of each kind that it may average him $68 per acre? Prove your results correct. Can there be another result?

Can you solve this problem from over 100 years ago?

Hint: the average number of acres sold at these prices is 1.75.