To find the equation for the graph of the proportional relationship between the cost (y) and the weight (x) of the roast beef, we need to determine the constant of proportionality.
Nigel paid $10 for 2 pounds of roast beef, so we can set up the relationship as follows:
\[ y = kx \]
Where:
- \(y\) is the cost,
- \(x\) is the weight in pounds, and
- \(k\) is the constant of proportionality (the cost per pound).
From the information given, we can substitute the values:
\[ 10 = k \cdot 2 \]
To solve for \(k\):
\[ k = \frac{10}{2} = 5 \]
Thus, the equation for the graph of the proportional relationship is:
\[ y = 5x \]
So, the final answer is:
y = 5x