i need help with a probability question

Question

anonymous · Answer

I can probably help you

anonymous · Answer

can you post ?

anonymous · Answer

oh your typing it. sry didnt see.

anonymous · Answer

my question is a test consists of 20 tru/false question to pass a student must answer 18 corectly .. if a student guesses on each question, what is the probability that the student will pass the test ?

anonymous · Answer

I think 40%

anonymous · Answer

Very close to zero, give me a minute to get the exact answer

anonymous · Answer

It is definitely not 40%.  Much lower

anonymous · Answer

can you tell me like how to get the answer

anonymous · Answer

it would help me alot

anonymous · Answer

probably. I totally forgot this subject.

anonymous · Answer

So...try getting the probability of one correct answer.  True or false.  That is 50%

anonymous · Answer

If you guess on a tru/false, thats 50 percent for each answer.

anonymous · Answer

so you use that and 20 get your percentage
then subtract 2
I think...

anonymous · Answer

Now try two answers correct.  He has to guess 50% correctly twice.  To answer two correct questions he has to get 50% twice

anonymous · Answer

To answer 18 correct he's have to be some kind of superhero

anonymous · Answer

so it will be like .50*.50 ?

anonymous · Answer

Dude this is really hard to think right now i'm totally stoned out of my mind

anonymous · Answer

.50*.50 18 times ?

anonymous · Answer

maybe its like .50 times 18

anonymous · Answer

maybe its like
.5^18

anonymous · Answer

OH NO NOW I REMEMBER

anonymous · Answer

what you have to do it find the probability of him NOT getting 18. And subtract that from 100%

anonymous · Answer

So in order to not get 18 correct he has to get three incorrect am i right?

anonymous · Answer

yea

anonymous · Answer

how do you find the probability of getting three incorrect?

anonymous · Answer

do you know any good way to get blood out of my keyboard? Its gotten to the point where its just nasty

anonymous · Answer

? what does that have 2 wid anething ?

anonymous · Answer

dude i don't know i'm just trying to help you maybe you could help me too

anonymous · Answer

get alcohol pads probably

anonymous · Answer

that actually sounds like a good idea actually has this worked for you in the past?

anonymous · Answer

dude just like find the prob. of getting three wrong then subtract. its very easy

anonymous · Answer

R u talkin bout my errors?