# Basic Probability Concepts

## Key Questions

• It's a matter of converting between a fraction and a percentage .

Remember that the word 'percent' really means 'per hundred'.
(and you are in fact converting from dollars to cents and back)

So if you have a probability of $0.11$ you can rewrite this as
0.11=11/100=11% (or $0.11=11 cents) And the other way around, if you have a chance-percentage of 45% you can rewrite this as: 45%=45/100=0.45 (or 45cents=$0.45)

The rule:
Fraction$\to$percentage = times 100
Percentage $\to$ fraction = divide by 100

That's all there is to it.

One more thing:
In probabilities you never have more than \$1 or 100%

In Probability we use the term Bernoullian trials for independent trials.

#### Explanation:

A sequence of trials are said to be Bernoullian if
(i) there are only two outcomes for each trial ( say a success or a failure)
(ii) Consecutive trials in the sequence are independent
and (iii) probability of success in every trial is a constant (namely p)
It is clear that no trial depends on the previous one here.
Consider drawing of two cards consecutively from a well shuffled deck of cards. Consider the event that cards are both diamonds. If the draw is with replacement the trials are independent ( Bernoullian) . Otherwise they are dependent.
In the former case the probability is ( 1/4) x (1/4)
In the later it is( 1/4) x (12/51)