To determine the equation for the proportional relationship between the cost of deli meat and its weight, we can start by identifying the variables:
Let \( C \) represent the cost in dollars and \( w \) represent the weight in pounds.
From the information provided, Nigel paid $10 for 2.5 pounds of roast beef. This gives us the following relationship:
\[ C = k \cdot w \]
where \( k \) is the constant of proportionality (the cost per pound).
To find \( k \), we can use the given information:
\[ 10 = k \cdot 2.5 \]
Now we can solve for \( k \):
\[ k = \frac{10}{2.5} = 4 \]
So the constant of proportionality \( k \) is 4, meaning the cost per pound is $4.
Now we can write the equation that models this relationship:
\[ C = 4w \]
This equation shows that the cost \( C \) in dollars is equal to $4 times the weight \( w \) in pounds.