The probability that your call to a service line is answered

The probability that your call to a service line is answered in less than 30 seconds is 0.75. Assume that your calls are incdependent. Assume that your calls are independent. What is the mean number of calls you must make until one is answered in less than 30 seconds? Is the random variable in the question continuous or discrete? Discrete Continuous No answer text provided No answer text provided.

Solution

It id discrete distribution problrm. Binomial distrbution is the key here.

Binomial Distribution

PMF of B.D is = f ( k ) = ( n k ) p^k * ( 1- p) ^ n-k
Where   
k = number of successes in trials
n = is the number of independent trials
p = probability of success on each trial