A submarine is diving at a depth of 500 meters. Every 3 minutes, it descends another 50 meters. It then reaches a depth of 1,000 meters.
How long did it take for the submarine to reach the depth of 1,000 meters?
The submarine descends 50 meters every 3 minutes, so it takes 3 minutes to descend 50 meters.
To reach a depth of 1,000 meters, the submarine needs to descend an additional 500 meters (1,000 - 500 = 500 meters).
Therefore, it takes 3 minutes x 500 meters/50 meters = 30 minutes to reach a depth of 1,000 meters. Answer: \boxed{30}.