# NCERT Class 12-Mathematics: Chapter –13 Probability Part 20

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**Question 86:**

The probability that a person is not a swimmer is . The probability that out of persons are swimmers is

(A)

(B)

(C)

(D)

**Answer: (A)**

**Question 87:**

The probability distribution of a discrete random variable X is given below:

The value of is

(A)

(B)

(C)

(D)

**Answer: (C)**

**Question 88:**

For the following probability distribution:

is equal to:

(A)

(B)

(C)

(D)

**Answer: (D)**

**Question 89:**

For the following probability distribution

is equal to

(A)

(B)

(C)

(D)

**Answer: (D)**

**Question 90:**

Suppose a random variable X follows the binomial distribution with parameters and , where . If is independent of and , then equals

(A)

(B)

(C)

(D)

**Answer: (A)**

**Question 91:**

In a college, students fail in physics, fail in mathematics and fail in both. One student is chosen at random. The probability that she fails in physics if she has failed in mathematics is

(A)

(B)

(C)

(D)

**Answer: (B)**

**Question 92:**

A and B are two students. Their chances of solving a problem correctly are and , respectively. If the probability of their making a common error is, and they obtain the same answer, then the probability of their answer to be correct is

(A)

(B)

(C)

(D)

**Answer: (D)**

**Question 93:**

A box has pens of which are defective. What is the probability that out of a sample of pens drawn one by one with replacement at most one is defective?

(A)

(B)

(C)

(D)

**Answer: (D)**