Final answer:
To find out the amount of salt needed for a tank that holds 400 gallons of water, we can set up a proportion using the information given. Solving for x, we find that 120 pounds of salt is needed.
Step-by-step explanation:
To find out how much salt is needed, we can set up a proportion. We know that the aquarium uses 3 pounds of salt for every 10 gallons of water. Let x represent the amount of salt needed for 400 gallons of water. The proportion would be: 3/10 = x/400. We can cross multiply to solve for x, which gives us: 3 * 400 = 10 * x. Simplifying this equation, we get: x = 1200/10 = 120 pounds of salt.
Learn more about Proportions in Mathematics