Need Help with Probability!!!

[daisymae]

Does anyone know what steps I should take for this problem???

Sixty percent of Americans believe that the government’s economic
stimulus package will result in major improvements by the 1st quarter of
2010. Out of the next 20 Americans interviewed,

(a) What is the probability that exactly 9 will believe that the
stimulus package will result in economic improvement?


(b) What is the probability that at least 9 will believe that the
stimulus package will result in economic improvement?

(c) What is the probability that no more than 9 will believe that
the stimulus package will result in economic improvement?

(d) How many would you expect to believe that the stimulus
package will result in economic improvement?

(e) What is the standard deviation in the number who believe that the stimulus package will result in economic
improvement?

 

[galactus]

Sixty percent of Americans believe that the government’s economic
stimulus package will result in major improvements by the 1st quarter of
2010. Out of the next 20 Americans interviewed,

It would appear this problem was written by a Democrat .

(a) What is the probability that exactly 9 will believe that the
stimulus package will result in economic improvement?

But, nonetheless, it is a binomial probability.

\(\displaystyle \binom{20}{9}(.60)^{9}(.40)^{11}\)

(b) What is the probability that at least 9 will believe that the
stimulus package will result in economic improvement?

At least 9 means we have to sum up the probabilities from 9 to 20

\(\displaystyle \sum_{k=9}^{20}\binom{20}{k}(.60)^{k}(.40)^{20-k}\)

(c) What is the probability that no more than 9 will believe that
the stimulus package will result in economic improvement?

Same as above except use k=0 to 9

(d) How many would you expect to believe that the stimulus
package will result in economic improvement?

\(\displaystyle {\mu}=np\)

(e) What is the standard deviation in the number who believe that the stimulus package will result in economic
improvement?

\(\displaystyle {\sigma}=\sqrt{np(1-p)}\)

 

[daisymae]

Thank you so much!

I agree.....just a little bit of bias in the problem.

 

[danville82]

I am a little confused about the difference between A and B. Can you further elaborate???


Thanks for your help!