Sum of binomial random variables

By convolution, the sum of two binomial distributions with the same probability of success is also a binomial distribution. Therefore, the pdf of V is binomial with n = 15 and p = 1/4. Similarly, the pdf of U is binomial with n = 5 and p = 1/4. To find the joint pdf of U and V, you can use a table or use the formula for the joint pdf of two independent random variables. The covariance of U and V can be found by using the formula for covariance.
  • #1
silentone
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Homework Statement



let y_1 and y_2 be iid bin(5,1/4) random variables

let v=y_1+2*y_2 and u = 3*y_1 -2y_2

find f_uv (u,v) and the cov(u,v)

Homework Equations



f_y (y) = (5 choose y) (1/4)^y (3/4)^5-x for x=0,1,2,3,4,5

covariance=E(uv)-E(u)E(v)

The Attempt at a Solution



By convolution the Sum of bin(n,p) and bin(m,p) = bin (n+m,p)

so pdf of v = bin(15,1/4) and pdf of u = bin (5,1/4)

The only way I know of to get the joint pdf is by a table. Is there a faster way?
 
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  • #2
For clarity, it's better to use the standard typecase: uppercase for names of r.v.s and lower case for values they take.
When U = u and V = v, what can you say about the values of Y1 and Y2?
 

What is the sum of binomial random variables?

The sum of binomial random variables is the result of adding together multiple independent binomial random variables. It is a discrete random variable that represents the total number of successes in a fixed number of independent trials, each with a binary outcome (usually defined as success or failure).

How is the sum of binomial random variables calculated?

The sum of binomial random variables can be calculated by adding together the individual probabilities of each outcome. This can be done using a mathematical formula or by using a binomial probability table. Alternatively, it can also be calculated using a computer program or statistical software.

What is the difference between the sum of binomial random variables and the binomial distribution?

The sum of binomial random variables is a specific value that represents the total number of successes in a fixed number of independent trials, while the binomial distribution is a probability distribution that describes the likelihood of each possible outcome in a binomial experiment. In other words, the sum of binomial random variables is a single number, while the binomial distribution is a set of probabilities.

What are some real-world applications of the sum of binomial random variables?

The sum of binomial random variables has many applications in various fields, including finance, genetics, and quality control. For example, it can be used to model the number of defective products in a batch, the number of successful trades in a stock portfolio, or the number of people in a population with a certain genetic trait.

What are some key properties of the sum of binomial random variables?

Some key properties of the sum of binomial random variables include: it is a discrete random variable, its mean is the product of the number of trials and the probability of success, its variance is the product of the number of trials, the probability of success, and the probability of failure, and it follows a binomial distribution. Additionally, the sum of binomial random variables can be approximated by a normal distribution under certain conditions (i.e. when the number of trials is large).

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