Question

Difficulty: MediumCalculating Distance

A coastal patrol boat is conducting a surveillance mission. It travels at a steady speed of 12 knots12\text{ knots} (nautical miles per hour) for 2 hours2\text{ hours} and 15 minutes15\text{ minutes}. It then increases its speed to 20 knots20\text{ knots} for 12 minutes12\text{ minutes} to intercept a vessel. What is the total distance traveled by the patrol boat, in nautical miles?

  1. A
    28.228.2
  2. 3131Answer
  3. C
    39.239.2
  4. D
    6767

Answer

The correct answer is 3131 nautical miles.
The total distance is found by calculating the distance for each leg separately. First, convert the times into hours: 15 minutes15\text{ minutes} is 0.25 hours0.25\text{ hours} (making the first leg 2.25 hours2.25\text{ hours}), and 12 minutes12\text{ minutes} is 0.2 hours0.2\text{ hours}. Multiplying these times by their respective speeds (12×2.2512 \times 2.25 and 20×0.220 \times 0.2) gives distances of 2727 and 44 nautical miles. Adding these together yields a total of 3131 nautical miles.

Step-by-Step Solution

1
Convert the time of the first leg into hours.
2 hours and 15 minutes=2+1560=2.25 hours2\text{ hours and } 15\text{ minutes} = 2 + \frac{15}{60} = 2.25\text{ hours}.
Speed is given in knots (nautical miles per hour), so the time must be in hours to cancel the units properly.
2
Calculate the distance traveled during the first leg.
12 knots×2.25 hours=27 nautical miles12\text{ knots} \times 2.25\text{ hours} = 27\text{ nautical miles}.
Using the formula Distance = Rate x Time.
3
Convert the time of the second leg into hours.
12 minutes=1260=0.2 hours12\text{ minutes} = \frac{12}{60} = 0.2\text{ hours}.
Maintaining consistent units across all calculations.
4
Calculate the distance traveled during the second leg.
20 knots×0.2 hours=4 nautical miles20\text{ knots} \times 0.2\text{ hours} = 4\text{ nautical miles}.
Using the formula Distance = Rate x Time for the second segment.
5
Add the distances of both legs to find the total distance.
27+4=31 nautical miles27 + 4 = 31\text{ nautical miles}.
The total distance is the sum of the individual segments of the journey.

Key Concept

Calculating total distance for multi-leg journeys requires converting mixed time units into hours and applying the Distance = Rate x Time formula to each leg separately.
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