The mean life-spans of various denominations of bills are shown in Table 11. For example, the mean life-span of a $1 bill is 1.5 years before it is taken out of circulation due to wear and tear.
Table 11 Mean Life-Spans of Denominations of Bills
Value of Bill (dollars)Life-span (years)
1…………………………………………………1.5
5…………………………………………………..2
10………………………………………………... 3
20…………………………………………………4
50…………………………………………………9
Let L be the mean life-span (in years) of a bill that is worth d dollars.
a. Identify the explanatory and response variables.
b. Which variable should be described by the horizontal axis of a coordinate system, L or d? How about the vertical axis?
c. Construct a scatterplot.
d. Is the association positive, negative or neither> What does that mean in this situation? Explain why this makes sense.
e. Each year, many more $1 bills are printed than $50 bills. Give at least two reasons why this makes sense.