It is given that
Number of times boundary was hit = 6
Total number of balls played = 30
So we get
Number of times boundary was not hit = 30 – 6 = 24
We know that
Probability that the batsman did not hit a boundary = number of times boundary was not hit/ total number of balls played
By substituting the values
Probability that the batsman did not hit a boundary = 24/30
By division
Probability that the batsman did not hit a boundary = 4/5 = 0.8