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Probability

The probability of a certain event is a number expressing the likelihood that a specific event will occur, expressed as the ratio of the number of actual occurrences to the number of possible occurrences. In mathematics, it is a measure of how often an event will happen and is the basis of statistics.

14,643 Questions

What is a biased coin probability?

A biased probability is one where not every outcome has the same chance of occurring. A biased coin is one where one side, the "heads" or "tails" has a greater probability than the other of showing.

A coin which has a centre of gravity closer to the tails side than the heads side would be biased in that heads is more likely to show than tails.

The size of coin can have an effect on the probability of heads and tails - during the Royal Institute Christmas lectures in the 1990s demonstrating probability a large version of the pound coin was made to be able to allow the audience to see it being tossed - on the broadcast (and tape) version it landed and stayed on its edge! showing the probability of heads = tails ≠ ½; the probability of heads = probability of tails, but they are actually slightly less than ½ as the coin could land on its edge and stay there - with a standard size coin, if it lands on its edge it takes very little for the centre of gravity to shift outside the base of the edge and for the coin to fall over, but with a very large similar coin (ie one scaled up [proportionally] in lengths) it can take quite a bit before the centre of gravity goes outside the base if it lands on its edge which forces it to fall over (plus there will be a "significant" rise in the centre of gravity to do so, thus favouring stability on an edge which does not exist in the standard, small, sized version of the coin).

What is the probability of picking a month that starts with J given that it ends in y?

The months that end in y are January, February, May, and July. Two of those four start with J. So 2/4=.5 is the answer.

What is the probability of an observation being above the mean?

For a continuous variable it is 0.5 but for a discrete variable the answer depends on the probability of the variable taking the mean value. It is half of the rest of the probability.

If the discrete variable X has mean m and Prob(X = m) is p

then Prob(X > m) = (1 - p)/2.

How do you make predictions using experimental probability?

Examples like the propability for raining tommorrow will 1/2 may or may not happen probability is called possibility

What is the purpose of finding standard deviation?

The standard deviation of a set of data is a measure of the random variability present in the data. Given any two sets of data it is extremely unlikely that their means will be exactly the same. The standard deviation is used to determine whether the difference between the means of the two data sets is something that could happen purely by chance (ie is reasonable) or not.

Also, if you wish to take samples of a population, then the inherent variability - as measured by the standard deviation - is a useful measure to help determine the optimum sample size.

What is the probability of drawing 3 black cards (spades or clubs) from a standard 52-card deck?

The probability of drawing three black cards from a standard pack depends on:

  • whether the cards are drawn at random,
  • whether or not the drawn cards are replaced before the next card is drawn,
  • whether the probability that is required is that three black cards are drawn after however many draws, or that three black cards are drawn in a sequence at some stage - but not necessarily the first three, or that the first three cards cards that are drawn are black.

There is no information on any of these and so it is not possible to be certain about the answer.

The probability of drawing three black cards, in three random draws - without replacement - from a standard deck, is 0.1176 approx.

What is the adjective form of probability?

Probabilistic is the adjective form of probability.

What is the probability that a randomly selected car is a two door hybrid?

The answer depends on where in the world the random selection is taken since the location will determine the mix of cars that the selection is made from.

What is the probability of rolling greater than 4?

Considering that a this is a six-faced die, the probability or rolling a 5 or 6 is 2/6. Or to simplify it, 1/3. This is because there are six sides, and you want to get two out of the six sides.

Is spinning a spinner and then rolling a die independent or dependent?

These are independent events; neither one depends on the results of the other.

What is favorable probability?

Favourable probability is the probability that the outcome that you are looking for does actually occur.

As an aside, "favourable" can be an unfortunate word if you are looking for the probability of an undesirable outcome - being the victim of a fatal incidence. Not many would consider that as being "favourable".

If you spin the wheel 5 times what is the probability of getting 100?

The answer will depend on what numbers are on the wheel, what the variable is (the sum, product or some other function of the individual spins). Since there is no information on these factors, the question cannot be answered.

What is the probability of not rolling a sum of 2 with two fair dice?

If you roll them often enough then the probability is 0. For just one roll, the probability is 35/36.

What is the probability of rolling the sum of 5 or 8 with 2 dice?

Recall that probabilty is the quotient of specific outcome divided by all outcomes. This is a relatively small problem to enumerate, so here goes...

1 + 1

2 + 1

3 + 1

4 + 1 = 5

5 + 1

6 + 1

1 + 2

2 + 2

3 + 2 = 5

4 + 2

5 + 2

6 + 2 = 8

1 + 3

2 + 3 = 5

3 + 3

4 + 3

5 + 3 = 8

6 + 3

1 + 4 = 5

2 + 4

3 + 4

4 + 4 = 8

5 + 4

6 + 4

1 + 5

2 + 5

3 + 5 = 8

4 + 5

5 + 5

6 + 5

1 + 6

2 + 6 = 8

3 + 6

4 + 6

5 + 6

6 + 6

You can see that the number of instances of the parent set is 36, while the number pf omstamces of the desired set is 9. As a result the probability of throwing a 5 or 8 with two dice is 9 in 36, or 1 in 4, or 0.25.

What are the odds of rolling doubles six times in a row?

Odds of rolling ONE six - 6:1

Odds of rolling TWO sixes - 36:1

Odds of rolling two sixes, SIX times - 216:1

What is the best definition of sample space of a probability event?

Not sure about the "best" definition. It is the set of all possible outcomes for the event.