Let’s take the value of X = $300
The average Y is $30.30
If pick one customer at random from the 10 customers corresponding to this income, the expenditure on lotto by that customer will not necessarily be equal to the mean value
“How do we explain the difference in expenditure of an individual customer in relation to income?”
The best we can do is to say that any individual’s expenditure on lotto is equal to the average value plus or minus some quantity