Which expression correctly represents the reciprocal heading for an initial heading less than 180 degrees?

Which expression correctly represents the reciprocal heading for an initial heading less than 180 degrees?

• A. INIT HDG + 180 - 20
• B. INIT HDG - 200 + 20
• C. INIT HDG + 200 - 20
• D. INIT HDG + 200 - 10

Answer: (C)

The heading you want is the reciprocal heading, which is simply the initial heading plus 180 degrees. When the starting heading is less than 180°, adding 180 stays below 360°, so no wrap-around is needed. Look at the expression that first adds 200 and then subtracts 20. Since 200 minus 20 equals 180, this form is effectively INIT HDG plus 180. That matches the rule for a reciprocal heading. For example, if the initial heading is 150°, the reciprocal heading should be 330°. Using this expression gives 150 + 200 − 20 = 150 + 180 = 330, which is correct. The other forms yield different totals (such as adding 160, subtracting 180, or adding 190), which do not equal INIT HDG + 180, so they don’t represent the reciprocal heading.

The heading you want is the reciprocal heading, which is simply the initial heading plus 180 degrees. When the starting heading is less than 180°, adding 180 stays below 360°, so no wrap-around is needed.

Look at the expression that first adds 200 and then subtracts 20. Since 200 minus 20 equals 180, this form is effectively INIT HDG plus 180. That matches the rule for a reciprocal heading. For example, if the initial heading is 150°, the reciprocal heading should be 330°. Using this expression gives 150 + 200 − 20 = 150 + 180 = 330, which is correct.

The other forms yield different totals (such as adding 160, subtracting 180, or adding 190), which do not equal INIT HDG + 180, so they don’t represent the reciprocal heading.