A N OTE TO THE R EADER The experimental or empirical probability of an event is based on what has actually happened while the theoretical probability of the event attempts to predict what will happen on the basis of certain assumptions. As the number of trials in an experiment, go on increasing we may expect the experimental and theoretical probabilities to be nearly the same. . Which of the following arguments are correct and which are not correct?
Give reasons for your answer. (i) If two coins are tossed simultaneously there are three possible outcomes—two heads, two tails or one of each. Therefore, for each of these outcomes, the probability is (ii) If a die is thrown, there are two possible outcomes—an odd number or an even number. Therefore, the probability of getting an odd number is .
. Summary In this chapter, you have studied the following points : . The theoretical (classical) probability of an event E, written as P(E), is defined as P (E) = Number of outcomes favourable to E Number of all possible outcomes of the experiment where we assume that the outcomes of the experiment are equally likely. .
The probability of a sure event (or certain event) is . . The probability of an impossible event is . .
The probability of an event E is a number P(E) such that P (E) . An event having only one outcome is called an elementary event. The sum of the probabilities of all the elementary events of an experiment is . .
For any event E, P (E) + P ( E ) = , where E stands for ‘not E’. E and E are called complementary events.