Sounds travels in sea water at the rate of 4,900 feet per second. Scientists can figure out the depth of the ocean floor by using a method called sonar.

Sonar measures the time it takes for sound waves to travel from a ship to the ocean floor and back.

Suppose a ship has a sonar sounding of 6 seconds. What would be the approximate depth of the ocean floor below the ship?

1. 1,630 feet
2. 4,900 feet
3. 9,800 feet
4. 14,700 feet

• Step 1: Understand the problem, what is being asked of you with this problem? You are asked to find the approximate depth of the ocean floor below the ship.
  
  
• Step 2: Analyze the information you are given. You know that sound travels at the rate of 4,900 feet per second through sea water. Sonar measures the time it takes sound waves to travel from the ship to the ocean floor and back.
  
  
• Step 3: Plan your problem solving strategy. You will want to find the number of feet by multiplying 4,900 by the 6 second reading. The second step to solving this problem will be to divide the answer in half as you have to remember that it is the time the sound travels from the ship to the floor and back to the ship. You only want the depth of the ocean floor.
  
  
• Step 4: Estimate a possible answer. Round the 4,900 feet to 5,000 feet and since you only need half of the six seconds because you only want one distance, multiply that 5,000 feet by 3 seconds (half of 6 seconds). Your estimate is 15,000 feet.
  
  
• Step 5: Solve the problem. Actually, you may already know the answer. As you look over the four choices, you see letter D is 14,700 feet which is very close to your estimate. Keep that in mind. Here is how you would solve it if you were to solve the problem all the way to a final answer.
  
  4,900 feet x 6 seconds = 29,400 feet
  
  29,400 feet divided by 2 = 14,700 feet
  
  
• Step 6: Now that you have an answer, check that answer. In this case you can compare it with your estimate of 15,000 feet. You are very close if not right on with your answers.
  
  Then check to see if 14,700 feet is one of your 4 choices for the question.