A letter or symbol is used to represent an unknown quantity
Answer:
or 
Step-by-step explanation:
Given



Required
Determine the probability of selecting Black and Red
First, we need to calculate the number of red and black balls
The probability is calculated as thus:

Convert to mathematical expressions
![Probability = [P(Black) *P(Red)] + [P(Red) *P(Black)]](https://tex.z-dn.net/?f=Probability%20%3D%20%5BP%28Black%29%20%2AP%28Red%29%5D%20%2B%20%5BP%28Red%29%20%2AP%28Black%29%5D)
Solve for each probaility;


So, we have:
![Probability = [P(Black) *P(Red)] + [P(Red) *P(Black)]](https://tex.z-dn.net/?f=Probability%20%3D%20%5BP%28Black%29%20%2AP%28Red%29%5D%20%2B%20%5BP%28Red%29%20%2AP%28Black%29%5D)
![Probability = [\frac{25}{100} *\frac{40}{100}] + [\frac{40}{100} *\frac{25}{100}]](https://tex.z-dn.net/?f=Probability%20%3D%20%5B%5Cfrac%7B25%7D%7B100%7D%20%2A%5Cfrac%7B40%7D%7B100%7D%5D%20%2B%20%5B%5Cfrac%7B40%7D%7B100%7D%20%2A%5Cfrac%7B25%7D%7B100%7D%5D)
![Probability = [\frac{1000}{10000}] + [\frac{1000}{10000}]](https://tex.z-dn.net/?f=Probability%20%3D%20%5B%5Cfrac%7B1000%7D%7B10000%7D%5D%20%2B%20%5B%5Cfrac%7B1000%7D%7B10000%7D%5D)
![Probability = [\frac{1}{10}] + [\frac{1}{10}]](https://tex.z-dn.net/?f=Probability%20%3D%20%5B%5Cfrac%7B1%7D%7B10%7D%5D%20%2B%20%5B%5Cfrac%7B1%7D%7B10%7D%5D)



or

Answer:
The answer is Discrete Random Variable
Step-by-step explanation:
A random variable is considered discrete if its possible values are countable.
In our case,
In a basketball game, for example, it is only possible for a team's score to be a whole number—no fractions or decimals are allowed, and so the score is discrete.
A good rule of thumb is this: if the variable you're measuring has to be rounded before it's written down, then it's continuous. If no rounding is necessary, as with anything that's countable, then it's discrete.
You add 1/4 each year:
800 to 1000 in one year
1000 to 1250 in 2
1250 to around 1812.5