The midpoints or class marks for the ages of the factory workers are 19.5, 29.5, 39.5, 49.5, 59.5 and 69.5. What are the class limits of this distribution??

Answer 1

Find the average of two adjacent midpoints; for example:
(29.5 + 39.5)/2 = 34.5
34.5 is the class boundary between the two classes whose midpoints are 29.5 and 39.5.
Drop and raise that value a half-point for the class limits:
34.5 - .5 = 34
34.5 + .5 = 35
Thus we have , so far:
Midpoint.....Class Limits
29.5........... ___ - 34
39.5 .......... 35 - ___
Work with more adjacent pairs of midpoints to fill in the rest of the class limits.