Question

A submarine cruising underwater started diving at a rate of 9 meters per minute. after 5 minutes, it was 180 meters below the surface of the water. how long after starting its descent was the submarine 360 meters below the surface?

Answer 1

Diving rate = 9 m/min
Let h = original depth,m

After 5 min, the depth is 180 m. Therefore
h + (9 m/min)*(5 min) = (180 m)
h + 45 = 180
h = 135 m

Let t min = time to reach a depth of 360 m.
Then
135 + (9 m/min)*(t min) = 360
9t = 225
t = 25 min

Answer: 25 minutes