# Provide the formula for mean all symbols. Question
Random variables Provide the formula for mean all symbols. 2021-02-26
It is known that, mean is the average value of a set of observation.
Assume a set of random variables X for size N, as $$X_{1}, X_{2},.....X_{n}$$.
Now, the mean of the set of random variables is defined as,
$$M = \frac{\sum x}{n}$$ where M is he mean,sum X defines the sum of all random variables of size N and N is the size of the set of random variables.

### Relevant Questions The length of time ,in minutes, for an airplane to obtain clearance for take off at a certainairport is a random variable Y=3X-2, where X has the density function
$$\displaystyle{f{{\left({x}\right)}}}={b}{e}{g}\in{\left\lbrace{c}{a}{s}{e}{s}\right\rbrace}{\frac{{{1}}}{{{4}}}}{e}^{{{\frac{{-{x}}}{{{4}}}}}},{x}{>}{0}\backslash{0},\text{else where}{e}{n}{d}{\left\lbrace{c}{a}{s}{e}{s}\right\rbrace}$$
Find the mean and variance of the random variable Y? For normal distribution with a mean of 278 and a standard deviation of 25, what is the Z value for a random value to be 185? For a population with a mean of $$\displaystyle\mu={100}$$ and a standard deviation of $$\displaystyle\sigma={20}$$,
Find the X values.
$$\displaystyle{z}=+{1.50}$$. For a population with a mean of $$\displaystyle\mu={100}$$ and a standard deviation of $$\displaystyle\sigma={20}$$,
Find the X values.
$$\displaystyle{z}=+{.75}$$. For a population with a mean of $$\displaystyle\mu={100}$$ and a standard deviation of $$\displaystyle\sigma={20}$$,
Find the X values.
$$\displaystyle{z}=+{1.80}$$. For a population with a mean of $$\displaystyle\mu={100}$$ and a standard deviation of $$\displaystyle\sigma={20}$$,
Find the X values.
$$\displaystyle{z}=-{.50}$$. For a population with a mean of $$\displaystyle\mu={100}$$ and a standard deviation of $$\displaystyle\sigma={20}$$,
Find the X values.
$$\displaystyle{z}=-{.40}$$. Random variable x represent the number of girls in a family of four children.
1) Construct a table describing the probability distribution, then find the mean and standard deviation. (Hint: List the different possible outcomes.)
2) Is it unusual for a family of four children to consist of four girls? $$\mu_{F} = 120$$ Independent random variables $$\displaystyle{X}_{{{1}}}{\quad\text{and}\quad}{X}_{{{2}}}$$ are combined according to the formula $$\displaystyle{L}={3}\cdot{X}_{{{1}}}+{2}\cdot{X}_{{{2}}}$$.
If $$\displaystyle{X}_{{{1}}}{\quad\text{and}\quad}{X}_{{{2}}}$$ both have a variance of 2.0, what is the variance of L?