# Thread: Random sample from a population.

1. ## Random sample from a population.

please please help me out for these question below. They are very important to me. As I am not good on Statistic and I don't have the model answers for them, I really want someone who can show me the answers about them. Therefore, I can check if i was doing the questions in the right way.

Thank you very much!!!

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Question 5---In a large population of N adults, let m be the number who are obese. The number N is known, but the number m is not known. A random sample of n people is chosen, where n is much smaller than N. Let X be the number of obese people in the sample.

(a) State the distribution of the random variable X. Hence write down the expectation and variance of X.
(b) Let Y = NX/n. Show that Y is an unbiased estimator of m.
(c) Find the standard deviation of Y .
(d) Suppose that N = 2, 000, 000 and n = 1, 000. To what accuracy should the estimate of m be reported?

2. (a) State the distribution of the random variable X. Hence write down the expectation and variance of X.

it is Binomial dist(n, $\displaystyle m/N$)
Expectation = $\displaystyle (nm)/N$
Variance = $\displaystyle ((nm)(N-m))/N^2$

(b) Let Y = NX/n. Show that Y is an unbiased estimator of m.
what is Y?
since it is random sampling we expect sample to have same characteristics as population
$\displaystyle (X/n)=m/N$

3. Originally Posted by rubic
(a) State the distribution of the random variable X. Hence write down the expectation and variance of X.

it is Binomial dist(n, $\displaystyle m/N$)
Expectation = $\displaystyle (nm)/N$
Variance = $\displaystyle ((nm)(N-m))/N^2$

(b) Let Y = NX/n. Show that Y is an unbiased estimator of m.
$\displaystyle (X/n)=m/N$