Quick
Answer:
Half of the items
are cheaper at the grocery store.
The convenience store’s prices seem
lower overall, however, due to the big difference in the
prices of seltzer.


Complete
Solution:
There are several ways to approach this
problem. For example, using the hint, draw the line y
= x on a copy of the graph. A
point below the line indicates that the item’s price
at the convenience store was less than its price at the
grocery store. For example, the point for Ginger
ale is below the line. It cost about $1.40 in the grocery
but only $1.00 in the convenience store. Four of the eight
points are below the line, indicating that the grocery
store was more expensive for half the items, while the
convenience store was more expensive for half the items.
Alternate Approcach
Another way to examine pricing at the two stores uses
the vertical distance from each
data point to the line y = x. On the scatterplot,
this distance represents the
difference in prices at the two stores. The
table below lists the estimated difference for each item
in the column for the store where it costs more. The sums
of the differences show that prices in the grocery store
are higher overall.

Approximate
Difference at Most Expensive Store 
Grocery 
Convenience 
Nestea™ 

$0.60 
Coke™ 

$0.50 
Sprite™ 

$0.40 
Pepsi™ 
$0.00 
$0.00 
Seltzer 
$1.60 

Evian™ 
$0.40 

Tonic 

$0.40 
Ginger
Ale 
$0.40 

Total 
$2.40 
$1.90 

