Final answer:
The amount of salt in the tank at the end of 40 minutes is 370 pounds.
Step-by-step explanation:
To find the amount of salt in the tank after 40 minutes, we need to calculate the net change in the amount of salt in the tank during that time. The tank initially contains 200 gallons of brine with 50 pounds of salt, and brine is flowing in and out of the tank at a rate of 4 gallons per minute. Since the salt concentration in the brine entering the tank is 2 pounds per gallon, the amount of salt entering the tank each minute is 4 gallons x 2 pounds = 8 pounds.
Therefore, the net change in the amount of salt in the tank after 40 minutes is 40 minutes x 8 pounds/minute = 320 pounds. Adding this to the initial amount of salt in the tank, we get 50 pounds + 320 pounds = 370 pounds of salt in the tank at the end of 40 minutes.