A submarine is patrolling the ocean. Each hour, it descends 25 feet and then ascends 10 feet. At 7:00 AM, it is at a depth of –100 feet. What will its depth be at 11:00 AM?

Answer 1

There is a net descent of 15 feet per hour. In 4 hours, there is a net descent of 60 feet. The depth will then be (-)160 feet.