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Ex.15.1 Q11 Probability Solution - NCERT Maths Class 9

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The blood groups of \(30\) students of Class VIII are recorded as follows:

\(A,\, B, \,O,\, O,\, AB,\, O,\, A,\, O,\,\\ B,\, A,\, O,\, B,\, A,\, O,\, O,\, A,\,\\ AB,\, O,\, A,\, A,\, O,\, O,\, AB,\,\\ B,\, A,\, O,\, B,\, A,\, B,\, O.\)

Use this table to determine the probability that a student of this class, selected at random, has blood group \(AB.\)

 Video Solution
Ex exercise-15-1 | Question 11

Text Solution

What is known?

No of students and their blood group.

What is unknown?

Probability of students having blood group \(AB.\)


The empirical probability \(P(E)\) of an event \(E\) happening, is given by:

\(\begin{align}{P}({E})=\frac{ \begin{pmatrix} \text { Number of trials in which }\\ \text{the event happened } \end{pmatrix} }{  \text { The total number of trials } }\end{align}\)

Use probability to derive the solution where

Probability (Of a selected student having a specific blood group)

\[\begin{align}\\&=\frac{ \begin{pmatrix}\text { Number of students having} \\ \text{ specific blood group} \end{pmatrix}}{\text { Total number of students }} \end{align}\]


Total no of students \(= 30\)

No of students having blood group \(AB = 3\)


Probability \(P\) (Of a student having blood group \(AB\))

\(\begin{align}\\&=\frac{ \begin{pmatrix} \text { Number of students having} \\ \text{ blood group }  AB \end{pmatrix} }{\text { Total number of students }} \\ &=\frac{3}{30} \\& =\frac{1}{10} \end{align}\)

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