# Probability check

• Jan 5th 2011, 04:45 AM
Mathematicsfan
Probability check
I came across this task, and I could not solve it furthermore.
Can anyone check my equation and help me solve it?

-The probability to succeed in a random test is 0.8. It's known that if N people attending to the test the probability that all of them will succeed is 0.4096.
A- Find N.

I was only able to do this equation (Bernouli's table)

$(N/K)*(0.8)^k*(0.2)$ $^n^-K=0.4096$
Can anyone help me solving furthermore with this equation please.
that's ^n-k
• Jan 5th 2011, 05:17 AM
alexmahone
Quote:

Originally Posted by Mathematicsfan
I came across this task, and I could not solve it furthermore.
Can anyone check my equation and help me solve it?

-The probability to succeed in a random test is 0.8. It's known that if N people attending to the test the probability that all of them will succeed is 0.4096.
A- Find N.

I was only able to do this equation (Bernouli's table)

$(N/K)*(0.8)^k*(0.2)$ $^n^-K=0.4096$
Can anyone help me solving furthermore with this equation please.
that's ^n-k

$(0.8)^N=0.4096$

Can you solve for N?
• Jan 5th 2011, 05:22 AM
Mathematicsfan
No, I don't know I tried desperately.
can you guide me ?
• Jan 5th 2011, 05:24 AM
alexmahone
Quote:

Originally Posted by mathematicsfan
no, i don't know i tried desperately.
Can you guide me ?

$(0.8)^N=0.4096$

$(0.8)^N=(0.8)^4$

Find N.
• Jan 5th 2011, 05:32 AM
Mathematicsfan
How did you get 4? cause that's the answer .
and where did the 0.2 ^n-k go ? and N\K ?
• Jan 5th 2011, 05:51 AM
alexmahone
Quote:

Originally Posted by Mathematicsfan
How did you get 4? cause that's the answer .
and where did the 0.2 ^n-k go ? and N\K ?

This is a very simple question which does not require the use of Bernoulli's tables. You're probably overthinking it.
• Jan 5th 2011, 06:09 AM
Mathematicsfan
then i don't know how to solve it.
can you help me with what to do next ?
• Jan 5th 2011, 06:13 AM
alexmahone
Quote:

Originally Posted by Mathematicsfan
then i don't know how to solve it.
can you help me with what to do next ?

I solved it for you in post #4. N=4.
• Jan 5th 2011, 06:13 AM
Mathematicsfan
lolllllllllllll I got it lollll
this is so easy wow.w
I just had to play with the Powers /
lol thanks a lot