SOLUTION: . A test consists of 10 multiple choice questions with five choices for each question. As an experiment,you GUESS on each and every answer without even reading the questions. What

Question 1033544: . A test consists of 10 multiple choice questions with five choices for each question. As an experiment,you GUESS on each and every answer without even reading the questions.
What is the probability of getting exactly 7 questions correct on this test?
Someone please help me, I cant wrap my head around this question. How do I go about finding "P"
I know n=10 r=7 p=? q=1-p

Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
p=0.2; q, or 1-p=0.8
exactly 7 questions right
10C7(0.2)^7(0.8)^3.
The 10C7 is the number of ways 7 questions can be answered correctly out of 10. It is 10!/7!3!=120
120*0.2^7*0.8^3=0.0008
For any number of questions right, use 0.2, which is the likelihood of guessing right with 5 choices, 1/5, and raise it to the number you want. Then use the complement of 0.2, or 0.8, and raise it to the number you want. The exponents must add up to the number of trials, in this instance 10.
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