🔍 Key Concepts

• Difference of longitude (DLo) and how to handle east longitudes vs west longitudes, especially when crossing the 180° meridian (International Date Line) • Parallel sailing formula: departure = DLo (in minutes of arc) × cosine of latitude • Relationship between course (east or west along a parallel) and the sign/direction of the longitude change

💭 Think About

• First, sketch or imagine the two positions on a simple world map: Are you east or west of the 180° meridian at the start and at the end? Which direction (east or west) are you really traveling? • Compute the numerical difference in longitude carefully: how do you convert longitudes on opposite sides of 180° into a usable DLo for parallel sailing? • Once you have the DLo in minutes of arc and the latitude, how do you use the parallel sailing formula to find the distance, and how does that distance compare to the answer choices?

✅ Before You Answer

• Be sure you correctly identify whether the vessel is moving east or west when going from 176°09'E to 178°46'W, considering that 180°E = 180°W • Confirm that your DLo is expressed in minutes of arc, not degrees, before applying the parallel sailing distance formula • Double-check that your final distance is consistent with the cosine of the common latitude (52°01'N) and that the chosen answer matches both your direction (course) and computed distance