A multiple-choice test has 7 questions each with 5 responses, one of which is correct. The lowest number of correct answers a student must obtain in order to receive a grade of A is 5. Find the probability of receiving an A by randomly and independently guessing at the correct answer.
2006-10-01 16:05:08 · 1 answers · asked by RunsLikeElijah 3 in Science & Mathematics ➔ Mathematics
To get an A, must get five or more correct answers.
.2 probability of getting any given answer.
So, we count the chances of getting five, six or seven.
7 equals (.2)^7 Every answer is right
6 = (.2)^6 * 7
5 = (.2)^5 * 42
Multiply them out and get the answer. The last term will dominate. .2 equals 1/5 (1/5)^5 = 1/3125
1/3125 * 42 = .01344
You've got about 1.5% chance of doing it. Good luck.
For the complete answer, multiply out all terms and sum them.
2006-10-01 16:19:59 · answer #1 · answered by John T 6 · 0⤊ 0⤋