Question

The blood groups of 30 students of class IX are recorded as follows:

A

B

O

O

AB

O

A

O

B

A

O

B

A

O

O

A

AB

O

A

A

O

O

AB

B

A

O

B

A

B

O

A student is selected at random from the class from blood donation, Fin the probability that the blood group of the student chosen is:
(i) A
(ii) B
(iii) AB
(iv) O

Answer 1

The total number of trials is 30.

Remember the empirical or experimental or observed frequency approach to probability.

If n be the total number of trials of an experiment and A is an event associated to it such that A happens in m-trials. Then the empirical probability of happening of event A is denoted by P (A) and is given by

P (A)=`m/n`

(i) Let A₁ be the event that the blood group of a chosen student is A.

The number of times A₁ happens is 9.

Therefore, we have

`P (A_1) = 9/30`

             =0.3

(iii) Let A₂ be the event that the blood group of a chosen student is B.

The number of times A₂ happens is 6.

Therefore, we have

`P (A-2) = 6/30`

             =0.2

(iii) Let A₃ be the event that the blood group of a chosen student is AB.

The number of times A₃ happens is 3.

Therefore, we have

`P (A_3) = 3/30`

             =0.1

(iv) Let A₄ be the event that the blood group of a chosen student is O.

The number of times A₄ happens is 12.

Therefore, we have

`P (A_4) = 12/30`

             =0.4