Question

The average rate of “set waves”, larger waves which come in a small group and are preferred by surfers, is 8 per 20 min.

a) What is the standard deviation of the number of waves per 20 min?

b) What is the probability of there being 18 waves in an hour?

Answer 1

(a) Let x be the no of set waves in 20 min, where x Po(8)

i.e. = 8

Mean = = = 8

Mean = 8

Standard deviation = = =

Standard deviation = 2.828

(b) Probability of 18 waves in an hour (60 min)

Let x be the no of set waves in 60 min, where x Po(8*3=24)

  

Probability of there being 18 waves in an hour = 0.04115