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# Ex.15.1 Q11 Probability Solution - NCERT Maths Class 9

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## Question

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
Probability
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 $$AB.$$

Reasoning:

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}

Steps:

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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