Question

200 elementary school students were surveyed to find their blood groups. Of those, 55 were of blood group A, 85 of blood group B, and 21 of blood group O.
What is the probability that a randomly chosen student has either blood group A or blood group B?
B) 0.60
C) 0.70
D) 0.81

Answer 1

The answer to your question is C)0.70

Answer 2

Answer:  The correct option is (C) 0.70.

Step-by-step explanation:  Given that 200 elementary school students were surveyed to find their blood groups, out of which 55 were of blood group A, 85 of blood group B and 21 of blood group O.

We are given to find the probability that a randomly chosen student has either blood group A or blood group B.

Let, S denotes the sample space for the experiment, so

n(S) = 200.

Let, E be the event of choosing  a student that has blood group A and F be the event choosing  a student that has blood group B.

Then, according to the given information, we have

$n(E)=55,~~n(F)=85.$

Since a student cannot have both the blood groups A and B, so

$n(E\cap F)=0.$

We have

The number of students that having either blood group A or B is given by

$n(E\cup F)=n(E)+n(F)-n(E\cap F)=55+85-0=140.$

Thus, the probability that a randomly chosen student has either blood group A or blood group B is

$P(E\cup B)=\dfrac{n(E\cup F)}{n(S)}=\dfrac{140}{200}=0.7.$

Required probability is 0.7.

Option (C) is CORRECT.