The following table shows the blood groups of $40$ students of a class:
BLOOD GROUP $A$ $A B$ $B$ $O$
NO. OF STUDENTS $9$ $5$ $11$ $15$
One student in the class is chosen at random. What is the probability that the chosen student has blood group: (i) $O$ ? (ii) $A B$ ?

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Solution

Given,
Total number of students in the class $= 40$
Let $E_{1}$ and $E_{2}$ event of choosing students having blood groups $O$ and $A B$
No. of students having blood group $O$ $(E_{1}) = 15$
No. of students having blood group $A B$ $(E_{2}) = 5$
Step 1: Find the probability of the student having a blood group $O$ .
Probability of favorable outcome $P = \frac{N o . o f f a v o u r a b l e o u t c o m e}{T o t a l n u m b e r s t u d e n t s}$
Probability of student who has $O$ blood group $P (E_{1}) = \frac{15}{40} = 0.375$
Step 2: Find the probability of the student having a blood group $A B$ .
Probability of student who has $A B$ blood group $P (E_{2}) = \frac{5}{40} = 0.125$
Hence, the probability of choosing the student has a blood group: (i) $O$ is $0.375$ (ii) $A B$ is $0.125$

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The following table shows the blood groups of 40 students of a class.

$\begin{matrix} Blood group & A & B & O & A B Number of students & 11 & 9 & 14 & 6 \end{matrix}$

One student of the class is chosen at random. What is the probability that the chosen studet has blood group (i) O? (ii) AB?

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