For example, in a deck of 52 cards, the probability of pulling one of the 13
hearts from the deck is much higher than the likelihood of pulling out the ace
of spades. To calculate an exact value for the probability of drawing a heart
from the deck, divide the number of hearts you could possibly draw by the total
number of cards in the deck.
Video Lesson - Probability of Dice
div>
In contrast, the possibility of drawing the single ace of spades from the deck
is:
After looking at these examples, you should be able to understand the general
formula for calculating probability. Let’s look at a more complicated example:
Joe has 3 green marbles, 2 red marbles, and 5 blue marbles. If all the marbles
are dropped into a dark bag, what is the probability that Joe will pick out a
green marble?
There are 3 ways for Joe to pick a green marble (since there are 3 different
green marbles), but there are 10 total possible outcomes (one for each marble in
the bag). Therefore, you can simply calculate the probability of picking a green
marble:
When calculating probabilities, always be careful to count all of the possible
favorable outcomes among the total possible outcomes.
The Range of Probability
The probability, P, of any event occurring will always be 0 = P =
1. A probability of 0 for an event means that the event will never
happen. A probability of 1 means the event will always occur. For example,
drawing a green card from a standard deck of cards has a probability of 0;
getting a number less than seven on a single roll of one die has a probability
of 1.
If you are ever asked to calculate probability on the Subject Math, you can
automatically eliminate any answer choices that are less than 0 or greater than
1.
The Probability That an Event Will Not Occur
Some Subject Math questions ask you to determine the probability that an event will
not occur. In that case, just figure out the probability of the event occurring,
and subtract that number from 1.
Probability an event will not occur = 1 - Probability an event occurring
Probability and Multiple Events
The most difficult Subject Math probability questions deal with the probability of
multiple events occurring. Such questions will always deal with independent
events—events whose probability is not dependent on the outcome of any other
event. For these questions, the probability of both events occurring is the
product of the outcomes of each event: P(A)× P(B), where P(A) is the probability of the first
event and P(B) is the probability of the second event.
For example, the probability of drawing a spade from a full deck of cards and
rolling a one with a six-sided die is the product of the probability of each
event.
The same principle can be applied to finding the probability of a series of
events. Take a look at the following problem:
A teacher keeps a jar full of different flavored jelly beans on her desk and
hands them out randomly to her class. But one particularly picky student likes
only the licorice-flavored ones. If the jar has 50 beans in all—15 licorice, 10
cherry, 20 watermelon, and 5 blueberry—what is the probability that the first
three jelly beans given out are licorice-flavored?
In order to find the probability of three consecutive events, you should first
find the probability of each event separately. The first jellybean has a 15/50
chance of being licorice-flavored. The second jellybean, however, is a different
story. There are now only 49 jelly beans left in the jar, so the probability of
getting another licorice-flavored one is 14/49. The
probability of getting a third licorice-flavored jellybean is 13/48.
The odds of getting three licorice jelly beans in a row is:
Next to display next topic in the chapter.
Mathematics Practice Questions
Video Lessons and 10 Fully Explained Grand Tests
Large number of solved practice MCQ with explanations. Video Lessons and 10 Fully explained Grand/Full Tests.