Jim weighs 74.2kg, Connie weighs 67.8kg and Jane weighs 69.4kg. What is the range in their weights?

Range is biggest possible difference, so we need to find the largest weight and the smallest weight given to us:
Heaviest = 74.2kg (Jim) Lightest = 67.8kg (Connie)

To find the difference take away the smallest(lightest) from the largest(heaviest):
74.2 -67.8

6.4

So the range is 6.4kg.