We explain briefly what is the probability and how it works.
The probability of an event is to determine how many times the event will occur, compared to how many times it will not happen
But this is only the short version. It is not formally correct, and is not the whole truth, but it’s a good start.
Percentage or decimal
Often we express the probabilities in the form of a percentage. Flipping a coin, we have a 50% chance of getting a cross. Will land tails half the time, and fifty percent is half of the one hundred percent.
Another way to express the probability is to use a decimal number between 0 and 1.
In our example, tossing a coin and getting cross with a probability of 0.5, since 0.5 is exactly halfway between 0 and 1.
This way of expressing the probability is used in the calculations of probabilities. Either way is fine to write in both ways, and move from one to another is easy, with a little ‘practice.
Example: roll a die
When you run a die, what is the probability of getting a six? Well, the die is symmetrical, so all sides are equal and all have the same chance to get out. In other words, all have the same probability. Calculate this probability “p” (a number between 0 and 1).
We also know that rolling a die, we must necessarily get a result, that has to come out to force one of the sides, then the sum of their probabilities is 1.
Combining these two pieces of information we know that p + p + p + p + p + p = 1. We conclude therefore that p = 1/6. Wanting to express this result in percentages, we have almost 17%.
This is the probability for each of the sides of the nut, thus also for the six.
We can conclude that the probability of receiving a six is ​​1/6, or 17%.
Example: get a card
If you distribute a card from a deck mixed, all the cards have the same probability of exit. Since there are 52 cards in the deck, the probability of receiving one in particular is 1/52, or nearly 2%.
Example: get a spade
If we fish a card from a deck full, what is the probability of receiving one of spades?
Solution: In the deck there are 52 cards, 13 of spades. Each of them has output probability equal to 1/52, as we have seen. If we add all these probabilities, we arrive at 13/52 = 1/4. Therefore, the probability of receiving a spade is 1/4, or 0.25, or even 25%.
Combining the probability of two events
Often necessary to calculate the probability that two events occur simultaneously. Knowing the probability of each of the two events, how do you find their combined probability?
Without going into technical details, here’s how. If an event has probability 0.3 and the other 0.5, the probability that comes in contact with both is 0.3 * 0.5 = 0.15.
To find the probability combined, simply multiply the individual probabilities.
The probability of a combined between two events
Another recurring issue concerns the probability that it happens one of two events.
For example, you have a flush draw and a straight draw, what is the probability of centrarne one?
In this case, the question is a bit ‘more complicated. To get the combined probability for these two events, you must use this formula:
P = 1 – (1 – x) * (1 – y)
Example: if an event has probability 0.3 and the other 0.5, the probability that it understood at least one of the two is 1 – (1 – 0.3) (1 – 0.5) = 0.65.
Therefore, the probability that at least one of two events happens is 0.65, or 65%,
Note that when searching for the probability that one of two events happens, the combined probability is higher compared to the single probability of each of the events involved.
On the contrary, as we have seen above, the probability that comes in contact with both events is always lower than the individual probability of each of the two.