Question

A binomial distribution has a 60% rate success.There are 18 trials
1) What is the probability that there will be at least 12 success?
2) What is the probability that there will be 12 failures ?
3) What is the expected number of successes?

Answer 1

\[P(x=X) = \left(\begin{matrix}n \\ X\end{matrix}\right)p^{X}*(1-p)^{n-X}\]
where
n=18
p = 0.6
For 1) X>=12, For 2) X =6

\[E(X) = n*p\]

Answer 2

for which part

Answer 3

3) I did
0.60*18= 10.8
the key is 10

Answer 4

ok, im getting 0.37 for 1)
did you add each one, X=12, X=13 ...X=18

Answer 5

for 3) 10.8 is correct must be a rounding thing

Answer 6

\[(\frac{18!}{(18-12)!12!})*0.6^{12} * 0.4^{18-12} =0.1655178\]

Answer 7

sorry
1) the key is 0.25

Answer 8

correct
unfortunately you have to do 13,14,15...18 too

Answer 9

oh ok

Answer 10

can you show me how ?

Answer 11

i can try..looks like i got it wrong too :)

Answer 12

what did they give for 2)
0.0145 ??

Answer 13

I can't get answer 0.25,the key may wrong ?

Answer 14

2) I don't have a key ,but show me how you do number 2

Answer 15

12 failures means 6 successes
Find P(x=6)

Answer 16

ok i did some double checking and as long as the question is worded correctly, you are right, the key must be wrong

Answer 17

ty, I hope the key is wrong