A student emailed me a question on homework this morning, and after working out the solution for myself and checking the answer in the back of the book and finding it different from mine, I am worried that I am missing something. I hope someone can confirm my suspicion that the book’s answer is wrong. Here goes:
My solution:
P(seam needs rework) = P(>= 1 rivet is defective) = 1 - P(all rivets are fine) = 1 - (1 - p)^25.
Then set
1 - (1 - p)^25 = 0.2 and solve for p. One obtains p = 0.00889.
The book’s answer is 0.06235.
I should note that Googling this problem results in solutions that lead to my answer, and that the problem is from a well-known textbook for engineering students that is now in its 7th edition. I can’t find any errata for the textbook, so I have no idea if the solution in the back of the book is just in error.