Final answer:
Betty would pay the same cost for a lobster dinner at both restaurants if the lobster weighs 5 kilograms, as determined by setting up and solving the equation 25 + 3x = 30 + 2x.
Step-by-step explanation:
To find the weight of the lobster at which the cost of dinner at both restaurants would be the same, we need to set up an equation where the total costs for each restaurant are equal. At the first restaurant, the cost is $25 for the meal plus $3 per kilogram for the lobster. At the second restaurant, the cost is $30 for the meal plus $2 per kilogram for the lobster. Let x be the weight of the lobster in kilograms.
The equation for the cost at the first restaurant is 25 + 3x and for the second restaurant it is 30 + 2x. To find the weight where both costs are equal, we set the equations equal to each other: 25 + 3x = 30 + 2x. Solving this equation for x, we subtract 2x from both sides to get x = 5.
Thus, Betty would pay the same cost for a lobster dinner at both restaurants if the lobster weighs 5 kilograms.