How is a bowler's average calculated?
For an example, Anil Kumble's test-match bowling average is 29.65. What does this number mean?
Bowling average = total given runs / wickets taken by bowler
Let's take an example of Anil Kumble. He has taken 619 wickets and given 18355 runs in Test. So his bowling average = 18355 / 619 = 29.65.
The bowling average indicates the number of runs given by a bowler to take a wicket. So Anil Kumble gave 29.65 runs for every single wicket in Test.