#### notes

The likelihood of something happening is called the probability.**Terms related to probability:****Experiment :** An activity which produces an outcome or result is called an experiment.

**random Experiment :** An Experiment in which exact outcome cannot be predicted in advance.

For example:

1) rolling a dice

2) Drawing a card from well-shuffled pack of playing cards

3) Tossing a coin**Trial :** Performing an experiment is called a trial.**Event :** Each possible outcomes of an experiment is called event.**Probability of an event :** In a random experiment if 'n' is the total number of trials, then the empirical probability of the event E is P(E).

P(E) =

`"Number of trials happened in which event happened" / " Total number of trials"`

i.e. P(E) =`"Number of trials happened in which event happened" / n `

The Probability of an event lies between 0 and 1 (0 and 1 inclusive).

#### Shaalaa.com | Probability Experimental Approach

#### Related QuestionsVIEW ALL [43]

To know the opinion of the students about the subject *statistics*, a survey of 200 students was conducted. The data is recorded in the following table.

Opinion | Number of students |

like | 135 |

dislike | 65 |

Find the probability that a student chosen at random

(i) likes statistics, (ii) does not like it

Three coins are tossed simultaneously 200 times with the following frequencies of different outcomes:-

Outcome | 3 heads | 2 heads | 1 head | No head |

Frequency | 23 | 72 | 77 | 28 |

If the three coins are simultaneously tossed again, compute the probability of 2 heads coming up.

Blood Group |
Number of Students |

A | 9 |

B | 6 |

AB | 3 |

O | 12 |

Total | 30 |

The above frequency distribution table represents the blood groups of 30 students of a class. Use this table to determine the probability that a student of this class, selected at random, has blood group AB.

1500 families with 2 children were selected randomly, and the following data were recorded:-

Number of girls in a family | 2 | 1 | 0 |

Number of families | 475 | 814 | 211 |

Compute the probability of a family, chosen at random, having

(i) 2 girls (ii) 1 girl (iii) No girl

Also check whether the sum of these probabilities is 1.

Concentration of SO_{2} (in ppm) |
Number of days (Frequency) |

0.00 − 0.04 | 4 |

0.04 − 0.08 | 9 |

0.08 − 0.12 | 9 |

0.12 − 0.16 | 2 |

0.16 − 0.20 | 4 |

0.20 − 0.24 | 2 |

Total | 30 |

The above frequency distribution table represents the concentration of sulphur dioxide in the air in parts per million of a certain city for 30 days. Using this table, find the probability of the concentration of sulphur dioxide in the interval 0.12 − 0.16 on any of these days.

A teacher wanted to analyse the performance of two sections of students in a mathematics test of 100 marks. Looking at their performances, she found that a few students got under 20 marks and a few got 70 marks or above. So she decided to group them into intervals of varying sizes as follows: 0 − 20, 20 − 30… 60 − 70, 70 − 100. Then she formed the following table:-

Marks | Number of students |

0 - 20 | 7 |

20 - 30 | 10 |

30 - 40 | 10 |

40 - 50 | 20 |

50 - 60 | 20 |

60 - 70 | 15 |

70 - above | 8 |

Total 90 |

(i) Find the probability that a student obtained less than 20 % in the mathematics test.

(ii) Find the probability that a student obtained marks 60 or above.