1 answer
(click or scroll down)
Let x be the weight of the roast beef in pounds.
The cost of the roast beef is 10 dollars for 2 1/2 pounds, so the cost per pound is 10/(2 1/2)=(10/2)/(5/2)=4/5.
The equation for the graph of this proportional relationship is y=(4/5)x. Answer: \boxed{y=(4/5)x}.