# Thread: binomial setting

1. ## binomial setting

At site with an ancient swamp, the bones from 20 brontosaur skeletons have been unearthed. The bones do not show any sign of disease or malformation. It is thought that these animals wandered into a deep area of the swamp and became trapped in the swamp bottom. The 20 left femur bones were located and 4 of these left femurs are to be randomly selected without replacement for DNA testing to determine gender.

1. Let X be the number out of the 4 selected left femurs that are from males. Based on how these bones were sampled, explain why the probability of X is NOT binomial.

Fixed number of trials
Prob. of success remains the same
trials are independent
either fail succeed

not sure what makes it NOT binomial though.

2. Suppose the group of 20 brontosaurs whose remains were found in the swamp had been made up of 10 males and 10 females. What is the probability that all 4 in the sample to be tested are male?

is this a (20 NCR 2) problem.. Im kinda stuck here as well.

3. The DNA testing revealed that all 4 femurs tested were from males. Based on this result and your answer from part (b), do you think that males and females were equally represented in the group of 20 brontosaurs stuck in the swamp? Explain

4) Is it reasonable to generalize your conclusion in question 3, pertaining to the group of 20 brontosaurs to the population of all brontosaurs? Explain why or why not.

Any help would be great it kinda leads into the next 2 questions, so.. yea!
Thank you if you are helping me!

2. Originally Posted by flyinhigh43
At site with an ancient swamp, the bones from 20 brontosaur skeletons have been unearthed. The bones do not show any sign of disease or malformation. It is thought that these animals wandered into a deep area of the swamp and became trapped in the swamp bottom. The 20 left femur bones were located and 4 of these left femurs are to be randomly selected without replacement for DNA testing to determine gender.

1. Let X be the number out of the 4 selected left femurs that are from males. Based on how these bones were sampled, explain why the probability of X is NOT binomial.

Fixed number of trials
Prob. of success remains the same Mr F says: Really? Even though you're sampling without replacement ....?

trials are independent
either fail succeed

not sure what makes it NOT binomial though.

2. Suppose the group of 20 brontosaurs whose remains were found in the swamp had been made up of 10 males and 10 females. What is the probability that all 4 in the sample to be tested are male?

is this a (20 NCR 2) problem.. Im kinda stuck here as well.

Mr F says: Use the hypergeometric distribution. Have you been taught it?

3. The DNA testing revealed that all 4 femurs tested were from males. Based on this result and your answer from part (b), do you think that males and females were equally represented in the group of 20 brontosaurs stuck in the swamp? Explain

4) Is it reasonable to generalize your conclusion in question 3, pertaining to the group of 20 brontosaurs to the population of all brontosaurs? Explain why or why not.

Any help would be great it kinda leads into the next 2 questions, so.. yea!
Thank you if you are helping me!
Your answer to (2) should let you answer (3). Then you should think about (4).

3. No we haven't been taught that. I looked it up and it look very unfimiliar.

I was thinking of doing a geometcdf, however not sure becuase we have males AND females.

Not quite sure what to make of this now.

I read you loud and clear on #1 thank you!

4. Originally Posted by flyinhigh43
No we haven't been taught that. I looked it up and it look very unfimiliar.

I was thinking of doing a geometcdf, however not sure becuase we have males AND females.

Not quite sure what to make of this now.

I read you loud and clear on #1 thank you!
Q2: $\displaystyle \frac{{10 \choose 4} \cdot {10 \choose 0}}{{20 \choose 4}}$.

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