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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 the probability of obtaining exactly four heads in five flips of a coin given that at least three are heads?

We can simplify the question by putting it this way: what is the probability that exactly one out of two coin flips is a head? Our options are HH, HT, TH, TT. Two of these four have exactly one head. So 2/4=.5 is the answer.

What is the probability of not drawing a spade from a standard deck of playing cards?

The answer depends on how many cards are drawn. If you draw 40 cards, the probability is 0.

The probability of not drawing a spade in a random draw of one card from a standard deck is 39/52 = 3/4.

What is the probability of a month of august having 5 mondays?

The simplistic answer is that August will have five Mondays if the month starts on a Saturday, Sunday or Monday. Three days out of the seven so the probability is 3/7 = 0.4286. However, that assumes that any day of the week is equally likely and that is not the case. The impact of leap years and their 2800-year cycle is to increase the probability to 0.43

Can the sum of 2 probabilities be greater than 1?

Yes but it is not possible to attach any interpretation to that. The addition of probabilities makes sense only if they are mutually exclusive outcomes of the same trial. If they are, then their sum cannot be greater than 1.

What is the probability of rolling 2 sixes in a row with a single die?

It is a certainty. If the die is rolled often enough, the probability that two consecutive rolls show a six is 1.

What is the probability of picking a spade out of a 52 card deck of cards?

One in four.

There are 52 cards in the deck; 13 cards in each of four suits. Spades is one of the four suits, so you have one chance in 4 of picking a spade from a shuffled deck.

What is the probability of the spinner not landing on 1 or 4?

The answer depends on the number of sides on the spinner and what numbers are on it.

What is the probability that you rolling factors of 3?

With a single roll of a fair die, the probability is 1/3.

What is joint probability function?

The joint probability function for two variables is a probability function whose domain is a subset of two dimensional space. The joint probability function for discrete random variables X and Y is given as

pr(x, y) = pr(X = x and Y = y). If X and Y are independent random variables then this will equal pr(X =x)*pr(Y = y).

For continuous variables, the joint funtion is defined analogously:

f(x, y) = pr(X < x and Y < y).

What are complementary events in probability?

Complementary events are events that are the complete opposite. The compliment of event A is everything that is not event A.

For example, the complementary event of flipping heads on a coin would be flipping tails.

The complementary event of rolling a 1 or a 2 on a six-sided die would be rolling a 3, 4, 5, or 6.

(The probability of A compliment is equal to 1 minus the probability of A.)

How is probability related to the area under the normal curve?

The Normal curve is a graph of the probability density function of the standard normal distribution and, as is the case with any continuous random variable (RV), the probability that the RV takes a value in a given range is given by the integral of the function between the two limits. In other words, it is the area under the curve between those two values.

What is the probability of getting sum 8 if you throw two dice?

You can get 8 with (2, 6), (3, 5), (4, 4), (5, 3) or (6, 2), each with a probability of (1/6)*(1/6) = 1/36

The the total probability is 5/36 = 0.1388... recurring.

What is the outcome of picking a month of the year and tossing a coin?

There are 24 possible outcomes:

January-Heads,

January-Tails,

February-Heads,

February-Tails,

March-Heads,

and so on.

How often is the probability of the complement of an event less than the probability of the event itself?

It depends on the events.

The answer is 0.5*(Total number of events - number of events with probability = 0.5)

That is, discount all events such that their probability (and that of their complement) is exactly a half.

Then half the remaining events will have probabilities that are greater than their complement's.

What is the number of distinguishable permutation of the letters in the word September?

September has 9 letter, of which one appears 3 times.

So the number of distinct permutations is 9!/3! = 120,960