What is the constant of proportionality of 40 nickels in a coin roll?

The constant of proportionality refers to the relationship between the number of items and their total value. In the case of 40 nickels, each nickel is worth $0.05, so the total value is 40 nickels × $0.05 = $2.00. Therefore, the constant of proportionality, which represents the value per nickel, is $0.05.