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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 |
(i) A
(ii) B
(iii) AB
(iv) O
Solution
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
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