A Navy coastal patrol boat is assigned a 360-nautical-mile mission. It navigates the first… — Armed Services Vocational Aptitude Battery (ASVAB)

A Navy coastal patrol boat is assigned a $360$ -nautical-mile mission. It navigates the first $120$ nautical miles through restricted waters at an average speed of $30$ knots. It then travels the remaining $240$ nautical miles through open ocean at an average speed of $40$ knots. Determine the boat's overall average speed for the entire mission.

Answer:The boat's overall average speed for the entire mission is 【36】 knots.

Answer

The overall average speed is 36 knots.

The correct overall average speed is determined by calculating the total distance covered (

360

nautical miles) divided by the total time taken (

10

hours). First, find the time for each leg:

120

nautical miles at

30

knots takes

4

hours, and

240

nautical miles at

40

knots takes

6

hours. The total time is

10

hours. Therefore, the average speed is

360 \div 10 = 36

knots.

Step-by-Step Solution

Calculate the time spent navigating the first segment.

4

hours

Time is equal to distance divided by speed (

120 \div 30 = 4

Calculate the time spent traveling the second segment.

6

hours

Time is equal to distance divided by speed (

240 \div 40 = 6

Calculate the total time for the entire mission.

10

hours

Adding the time from both segments gives the total mission time (

4 + 6 = 10

Calculate the overall average speed.

36

knots

Overall average speed is the total distance divided by the total time (

360 \div 10 = 36

Key Concept

To find overall average speed for a trip with multiple segments, divide the total distance by the total time, rather than averaging the individual speeds.

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