Given:
Usual cost of a bottle of sparkling water = $1.69 each
This week they are on sale for 4 for $5.
To find:
Did you pay more or less for the bottle this week?
Solution:
We have,
Usual cost of 1 bottle = $1.69
On sale, cost of 4 bottles = $5
On sale, cost of 1 bottles =

= $1.25
Since, $1.25 is less than $1.69, therefore the unit cost on sale is less than usual unit cost.
Hence, you pay less for the bottle this week.