- Thread starter Dragan8ng
- Start date

- Joined
- Jun 18, 2007

- Messages
- 22,083

Please show us what you have tried andSo it says there is a 5% of a test being incorrect, so if we try 20 cases what is the probability of it being incorrect less than 3 times?

Please follow the rules of posting in this forum, as enunciated at:

Please

- Joined
- Apr 12, 2005

- Messages
- 10,912

Give it another go. Given 20 tests, there is SOME probability that the test will be wrong ALL 20 times! There is also some probability that it will be correct EVERY time.So the chance of it happening is 1/20 which = 0.05, so to get less than 3 it is 1-0,05 which = 0,95?

Given just one test, probabilities are 5% incorrect and 95% correct.

Given two tests, consider (0.05 + 0.95)^2

This should lead you on a trail of discovery.

It would help us help you if you told us up front that you are studying particular material, such as perhaps the Binomial Distribution.

Doesn't make sense to me, Im studying descriptive statistics, probability, random variables, trust intervals, testing parametrial hypothesis, regression and correlation, linear trend and individual indexes which is part of business statisticsGive it another go. Given 20 tests, there is SOME probability that the test will be wrong ALL 20 times! There is also some probability that it will be correct EVERY time.

Given just one test, probabilities are 5% incorrect and 95% correct.

Given two tests, consider (0.05 + 0.95)^2

This should lead you on a trail of discovery.

It would help us help you if you told us up front that you are studying particular material, such as perhaps the Binomial Distribution.

- Joined
- Jun 18, 2007

- Messages
- 22,083

What is the probability that - out of 20 tests - 0 (none) will be incorrect?So it says there is a 5% of a test being incorrect, so if we try 20 cases what is the probability of it being incorrect less than 3 times?

That confuses me even moreWhat is the probability that - out of 20 tests - 0 (none) will be incorrect?

- Joined
- Dec 30, 2014

- Messages
- 8,030

What do you find so special about 3 to say the probability of it being incorrect less than 3 times is .05?

Would you say the same answer for the probability of it being incorrect less than 2 times?

How about he probability of it being incorrect less than 5 times?

These probabilities can't all be the same. Do you see that?

Do you understand what less than 3 times in this problem?

I will do a part of this problem for you.

p(exactly 2 being incorrect out of 20) =_{20}C_{2}(.05)^{2}(.95)^{18} .................... edited

Would you say the same answer for the probability of it being incorrect less than 2 times?

How about he probability of it being incorrect less than 5 times?

These probabilities can't all be the same. Do you see that?

Do you understand what less than 3 times in this problem?

I will do a part of this problem for you.

p(exactly 2 being incorrect out of 20) =

Last edited by a moderator:

It's: 0,36, 0,38 and 0,19, so id guess it being less than 3 is the sum of all of those which = 0,93?Please calculate for X = 0, 1, 2. You tell me why.

- Joined
- Dec 30, 2014

- Messages
- 8,030

Don't round so much but your numbers are correct.It's: 0,36, 0,38 and 0,19, so id guess it being less than 3 is the sum of all of those which = 0,93?

- Joined
- Apr 12, 2005

- Messages
- 10,912

That's the spirit. Now, listen to Jomo.It's: 0,36, 0,38 and 0,19, so id guess it being less than 3 is the sum of all of those which = 0,93?

- Joined
- Jun 18, 2007

- Messages
- 22,083

Did you mean to say:What do you find so special about 3 to say the probability of it being incorrect less than 3 times is .05?

Would you say the same answer for the probability of it being incorrect less than 2 times?

How about he probability of it being incorrect less than 5 times?

These probabilities can't all be the same. Do you see that?

Do you understand what less than 3 times in this problem?

I will do a part of this problem for you.

p(exactly 2 being incorrect out of 20) =_{20}C_{2}(.05)^{2}(.95)^{15}

p(exactly 2 being incorrect out of 20) =