Please can Any One Help?
I throw darts repeatedly. Assume that on each single throw, my chance of hitting the bulls eye is 10%, independently of all other throws. I decide to throw until I have hit the bulls eye 3 times. What is the chance that I throw exactly 30 times? My Solusion
The third success' My solutions: occurs on the 30th trial if and only if there are exactly 2 successes in the first 29 trials, and then a success on the 30th. If p is the probability of success on any trial, here 0.1, then the probability of 2 successes in 29 trials is: (29C2)*p^2 * (1−p)^27=
=(406)*(0.10^2)*(1-0.10)^27 = 0.23609
probability of success on the 30th trial = 0.1 0.2360*0.1=0.0236

Question

Please can Any One Help?
I throw darts repeatedly. Assume that on each single throw, my chance of hitting the bulls eye is 10%, independently of all other throws. I decide to throw until I have hit the bulls eye 3 times. What is the chance that I throw exactly 30 times? My Solusion
The third success' My solutions: occurs on the 30th trial if and only if there are exactly 2 successes in the first 29 trials, and then a success on the 30th. If p is the probability of success on any trial, here 0.1, then the probability of 2 successes in 29 trials is: (29C2)*p^2 * (1−p)^27=
=(406)*(0.10^2)*(1-0.10)^27 = 0.23609
 probability of success on the 30th trial = 0.1 0.2360*0.1=0.0236

anonymous · Answer

Can some one solve the following problem please


On a true-false test, each question has exactly one correct answer: true, or false. A student knows the correct answer to 70% of the questions on the test. Each of the remaining answers she guesses at random, independently of all other answers. After the test has been graded, one of the questions is picked at random. Given that she got the answer right, what is the chance that she knew the answer?

anonymous · Answer

probability of 2 successes in 29 trials =0.2360
probability of success on the 30th trial = 0.1

0.2360*0.1=0.0236

anonymous · Answer

ANSWER IS 0.8235