Page 1 - Xl-CH-16-LESSON NOTE

XI - CHAPTER-16
PROBABILITY

KEY NOTES:

EXPERIMENT:

An experiment is defined as a process whose result is well defined .

RANDOM EXPERIMENT:

It is experiment whose outcomes are known, but it s not possible to predict the extract
outcome in advance

For example: (i) A coin is tossed (ii) A die is rolled

OUTCOMES:

A possible result of a random experiment is called an outcome. Each repetition of
experiment is called a trial.

SAMPLE SPACE:

The set of all possible outcomes of a random experiment is called the simple space and
is usually denoted by S. Sample space for the experiment of tossing a coin is { H,T } or a
rolling a die is { 1,2,3,4,5,6 }. Each element of a sample space is called a simple point. In

other words outcome of the random experiment is called a sample point.

Example 1: A coin is tossed three times

Solution: A coin is tossed is three times then

S = {HHH, HHT, HTH, THH, TTH, THT, HTT, TTT}

Example 2: A coin is tossed and a die is thrown

Solution: A coin is tossed then = {H, T}
1

A die is thrown then = {1, 2, 3, 4, 5, 6}
2
Hence S = {H1 , H2 , H3 ,H4 ,H5 ,H6 , T1 ,T2 ,T3 ,T4 ,T5 ,T6}

EVENT: Any subset of sample space S is called an event.