A marksman's chance of hitting a target with each of his shots is 60%. (Assume that the shots are independent of each other.) If he fires 30 shots, what is the probability of his hitting the target at least 20 time?
First, I found the mean by multiplying the trials by the probability of successes (.60 by 30) and received 18. Then I found the standard deviation (square root of 30x.60x.40), square root of npq and received the answer 2.68. Then I set up my equation as (19.5-18/2.68. 19.5 because I was told to not use 18, as x should be greater than or equal to 5 I believe.) I got the answer 0.56. Then I looked up my answer on the z score table and found .7123 but I am not sure if this whole process is correct.
1 answer
http://davidmlane.com/hyperstat/z_table.html