A frequency polygon drawn for the lifespans of a brand of light-bulbs uses the following class mid-points (in hours) and their frequencies:
(a) Class mid-points (hours): 700, 900, 1100, 1300, 1500
(b) Corresponding frequencies: 6, 14, 25, 9, 2
(c) (i) Identify the class interval that contains the lowest observed lifespan and the one that contains the highest observed lifespan.
(d) (ii) Using the information in part (i), calculate the range of the lifespans represented by the data.