probability of passing an exam is let's say 0.8, then what's probability of 10 people passing the exam, what's probability of 9 people passing the exam? Now I know this is binomial probability distribution and this is my solution a) (0.8)^{10} = 0.1073741824, b)(0.8)^9 * (0.2) = 0.0268435456

lemondedeninaug

lemondedeninaug

Answered question

2022-09-10

Probability of passing an exam is let's say 0.8, then what's probability of 10 people passing the exam, what's probability of 9 people passing the exam?
Now I know this is binomial probability distribution and this is my solution
a) ( 0.8 ) 10 = 0.1073741824 , b ) ( 0.8 ) 9 ( 0.2 ) = 0.0268435456
but most of my friends tell me the solution to b is: b) C ( 10 , 9 ) [ ( 0.8 ) 9 ( 0.2 ) ] = 0.268435456
so I don't really understand how is the 2nd probability higher than the 1st one, and why do we do that?

Answer & Explanation

Nodussimj

Nodussimj

Beginner2022-09-11Added 14 answers

Step 1
If you mean that 10 students are to be randomly selected, the reason why we have ( 10 9 ) ( = C ( 10 , 9 ) ). Because there are 10 arrangements of the people who pass the exams. Our outcomes are strings of length 10 like for example 1111111110 where 1 means passing the exam and 0 means not passing.
Step 2
Now, to answer your question: In how many ways can you place one 0 and 9 1's in a string? Well that is certainly ( 10 9 ) = 10. Therefore, the desired probability is ( 10 9 ) 0.8 9 0.2

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