If I remember correctly even in the ATPL syllabus you are definately NOT required to calculate the distance between two points that neither lie on the same meridian or on the same parallel.

However these points might (or might not )prove useful:

1)1 degree of latitude along any meridian will always represent 60 nm.

2)1 degree of longitude will ONLY represent 60 nm at the equator.The distance will vary as the cosine of the latitude.

3)The DEPARTURE FORMULA (the formula relating change of longitude to distance is ;

DEPARTURE DISTANCE(NM)=DIFF IN LONG(MINS)*COS LAT.

If you use the average latitude with this you get an answer that is roughly correct.

Remember that this formula is really only accurate if both points are at the same lat and therefore by definition is a Rhumb line distance.

Hope this is of some help,

Cheers AUTOTHROTTLE