Question

Every day Jo practices her tennis serve by continually serving until she has had a total of 50 successful serves. If each of her serves is, independently of previous ones, successful with probability .4 , .4, approximately what is the probability that she will need more than 100 100 serves to accomplish her goal?

Answer 1

Answer: 1

Step-by-step explanation:

Probability of Success = 0.4

Let (X) be the number of total successful serves she must practice continuously until she has 50 successful serves.

Therefore, to determine the successful practices to have 50 successful serves;

Probability of Success × (X) = 50

0.4 × X = 50

X= 50/0.4 ; X= 125

She MUST practice up to 125 serves to get the required 50 successful serves

Therefore, the probability that she need more than 100 serves to accomplish her goal = 1

METHOD 2

Probability = number of required outcomes / number of possible outcomes

Required outcome = >100 serves = 1

Possible outcomes = if she must serve at least 125 times to get 50 which means 1

Probably (P) = 1/1

= 1