🔍 Key Concepts

• Difference of longitude (DLo) and how to convert between degrees and minutes of arc • Parallel sailing formula: departure = DLo (in minutes of arc) × cos(latitude) • Relationship between departure (in minutes of arc) and distance in nautical miles along a parallel

💭 Think About

• First, how do you correctly find the numerical difference in longitude between 166°36.0'E and 157°54.0'W when they are on opposite sides of the 180° meridian? • Once you have DLo in degrees, how do you convert it into minutes of arc before using it in the parallel sailing formula? • After calculating the departure in minutes, what simple conversion lets you express that value as nautical miles, and how does that compare with the answer choices?

✅ Before You Answer

• Be sure you treat east and west longitudes on opposite sides of 180° correctly when finding DLo • Confirm that you convert degrees of longitude to minutes before multiplying by cos(latitude) • Use the cosine of the given latitude (19°54.0'N), not some rounded or nearby whole degree, when applying the formula