# NCERT Solutions for Class 11 Maths Maths Chapter 16

## Probability Class 11

### Exercise 16.1 : Solutions of Questions on Page Number : 386

Q1 :

Describe the sample space for the indicated experiment: A coin is tossed three times.

A coin has two faces: head (H) and tail (T).

When a coin is tossed three times, the total number of possible outcomes is 23 = 8

Thus, when a coin is tossed three times, the sample space is given by:

S = {HHH, HHT, HTH, HTT, THH, THT, TTH, TTT}

Q2 :

Describe the sample space for the indicated experiment: A die is thrown two times.

When a die is thrown, the possible outcomes are 1, 2, 3, 4, 5, or 6.

When a die is thrown two times, the sample space is given by S = {(x, y): x, y = 1, 2, 3, 4, 5, 6}

The number of elements in this sample space is 6 Ã— 6 = 36, while the sample space is given by:

S = {(1, 1), (1, 2), (1, 3), (1, 4), (1, 5), (1, 6), (2, 1), (2, 2), (2, 3), (2, 4), (2, 5), (2, 6), (3, 1), (3, 2), (3, 3), (3, 4), (3, 5), (3, 6), (4, 1), (4, 2), (4, 3), (4, 4), (4, 5), (4, 6), (5, 1), (5, 2), (5, 3), (5, 4), (5, 5), (5, 6), (6, 1), (6, 2), (6, 3), (6, 4), (6, 5), (6, 6)}

Q3 :

Describe the sample space for the indicated experiment: A coin is tossed four times.

Q4 :

Describe the sample space for the indicated experiment: A coin is tossed and a die is thrown.

Q5 :

Describe the sample space for the indicated experiment: A coin is tossed and then a die is rolled only in case a head is shown on the coin.

Q6 :

2 boys and 2 girls are in Room X, and 1 boy and 3 girls in Room Y. Specify the sample space for the experiment in which a room is selected and then a person.

Q7 :

One die of red colour, one of white colour and one of blue colour are placed in a bag. One die is selected at random and rolled, its colour and the number on its uppermost face is noted. Describe the sample space.

Q8 :

An experiment consists of recording boy-girl composition of families with 2 children.

(i) What is the sample space if we are interested in knowing whether it is a boy or girl in the order of their births?

(ii) What is the sample space if we are interested in the number of girls in the family?

Q9 :

A box contains 1 red and 3 identical white balls. Two balls are drawn at random in succession without replacement. Write the sample space for this experiment.

Q10 :

An experiment consists of tossing a coin and then throwing it second time if a head occurs. If a tail occurs on the first toss, then a die is rolled once. Find the sample space.

Q11 :

Suppose 3 bulbs are selected at random from a lot. Each bulb is tested and classified as defective (D) or non-defective (N). Write the sample space of this experiment?

Q12 :

A coin is tossed. If the out come is a head, a die is thrown. If the die shows up an even number, the die is thrown again. What is the sample space for the experiment?

Q13 :

The numbers 1, 2, 3 and 4 are written separately on four slips of paper. The slips are put in a box and mixed thoroughly. A person draws two slips from the box, one after the other, without replacement. Describe the sample space for the experiment.

Q14 :

An experiment consists of rolling a die and then tossing a coin once if the number on the die is even. If the number on the die is odd, the coin is tossed twice. Write the sample space for this experiment.

Q15 :

A coin is tossed. If it shows a tail, we draw a ball from a box which contains 2 red and 3 black balls. If it shows head, we throw a die. Find the sample space for this experiment.

Q16 :

A die is thrown repeatedly until a six comes up. What is the sample space for this experiment?

### Exercise 16.2 : Solutions of Questions on Page Number : 393

Q1 :

A die is rolled. Let E be the event â€œdie shows 4â€ and F be the event â€œdie shows even numberâ€. Are E and F mutually exclusive?

Q2 :

A die is thrown. Describe the following events:

(i) A: a number less than 7 (ii) B: a number greater than 7 (iii) C: a multiple of 3

(iv) D: a number less than 4 (v) E: an even number greater than 4 (vi) F: a number not less than 3

Also find Q3 :

An experiment involves rolling a pair of dice and recording the numbers that come up. Describe the following events:

A: the sum is greater than 8, B: 2 occurs on either die

C: The sum is at least 7 and a multiple of 3.

Which pairs of these events are mutually exclusive?

Q4 :

Three coins are tossed once. Let A denote the event ‘three heads showâ€, B denote the event â€œtwo heads and one tail showâ€. C denote the event â€œthree tails showâ€ and D denote the event ‘a head shows on the first coinâ€. Which events are

(i) mutually exclusive? (ii) simple? (iii) compound?

Q5 :

Three coins are tossed. Describe

(i) Two events which are mutually exclusive.

(ii) Three events which are mutually exclusive and exhaustive.

(iii) Two events, which are not mutually exclusive.

(iv) Two events which are mutually exclusive but not exhaustive.

(v) Three events which are mutually exclusive but not exhaustive.

Q6 :

Two dice are thrown. The events A, B and C are as follows:

A: getting an even number on the first die.

B: getting an odd number on the first die.

C: getting the sum of the numbers on the dice â‰¤ 5

Describe the events

(i) (ii) not B (iii) A or B

(iv) A and B (v) A but not C (vi) B or C

(vii) B and C (viii) Q7 :

Two dice are thrown. The events A, B and C are as follows:

A: getting an even number on the first die.

B: getting an odd number on the first die.

C: getting the sum of the numbers on the dice â‰¤ 5

(i) A and B are mutually exclusive

(ii) A and B are mutually exclusive and exhaustive

(iii) (iv) A and C are mutually exclusive

(v) A and are mutually exclusive

(vi) are mutually exclusive and exhaustive.

### Exercise 16.3 : Solutions of Questions on Page Number : 403

Q1 :

Which of the following can not be valid assignment of probabilities for outcomes of sample space S = Assignment Ï‰1 Ï‰2 Ï‰3 Ï‰4 Ï‰5 Ï‰6 Ï‰7 (a) 0.1 0.01 0.05 0.03 0.01 0.2 0.6 (b)       (c) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 (d) â€“0.1 0.2 0.3 0.4 â€“0.2 0.1 0.3 (e)       Q2 :

A coin is tossed twice, what is the probability that at least one tail occurs?

Q3 :

A die is thrown, find the probability of following events:

(i) A prime number will appear,

(ii) A number greater than or equal to 3 will appear,

(iii) A number less than or equal to one will appear,

(iv) A number more than 6 will appear,

(v) A number less than 6 will appear.

Q4 :

A card is selected from a pack of 52 cards.

(a) How many points are there in the sample space?

(b) Calculate the probability that the card is an ace of spades.

(c) Calculate the probability that the card is (i) an ace (ii) black card.

Q5 :

A fair coin with 1 marked on one face and 6 on the other and a fair die are both tossed. Find the probability that the sum of numbers that turn up is (i) 3 (ii) 12

Q6 :

There are four men and six women on the city council. If one council member is selected for a committee at random, how likely is it that it is a woman?

Q7 :

A fair coin is tossed four times, and a person win Re 1 for each head and lose Rs 1.50 for each tail that turns up. From the sample space calculate how many different amounts of money you can have after four tosses and the probability of having each of these amounts.

Q8 :

Three coins are tossed once. Find the probability of getting

(vii) exactly two tails (viii) no tail (ix) at most two tails.

Q9 :

If is the probability of an event, what is the probability of the event ‘not A’.

Q10 :

A letter is chosen at random from the word ‘ASSASSINATION’. Find the probability that letter is (i) a vowel (ii) an consonant

Q11 :

In a lottery, person choses six different natural numbers at random from 1 to 20, and if these six numbers match with the six numbers already fixed by the lottery committee, he wins the prize. What is the probability of winning the prize in the game? [Hint: order of the numbers is not important.]

Q12 :

Check whether the following probabilities P(A) and P(B) are consistently defined

(i) P(A) = 0.5, P(B) = 0.7, P(A âˆ© B) = 0.6

(ii) P(A) = 0.5, P(B) = 0.4, P(A âˆª B) = 0.8

Q13 :

Fill in the blanks in following table:

 P(A) P(B) P(A âˆ© B) P(A âˆª B) (i)   â€¦ (ii) 0.35 â€¦ 0.25 0.6 (iii) 0.5 0.35 â€¦ 0.7

Q14 :

Given P(A) = and P(B) = . Find P(A or B), if A and B are mutually exclusive events.

Q15 :

If E and F are events such that P(E) = , P(F) = and P(E and F) = , find:(i) P(E or F), (ii) P(not E and not F).

Q16 :

Events E and F are such that P(not E or not F) = 0.25, State whether E and F are mutually exclusive.

Q17 :

A and B are events such that P(A) = 0.42, P(B) = 0.48 and P(A and B) = 0.16. Determine (i) P(not A), (ii) P (not B) and (iii) P(A or B).

Q18 :

In Class XI of a school 40% of the students study Mathematics and 30% study Biology. 10% of the class study both Mathematics and Biology. If a student is selected at random from the class, find the probability that he will be studying Mathematics or Biology.

Q19 :

In an entrance test that is graded on the basis of two examinations, the probability of a randomly chosen student passing the first examination is 0.8 and the probability of passing the second examination is 0.7. The probability of passing at least one of them is 0.95. What is the probability of passing both?

Q20 :

The probability that a student will pass the final examination in both English and Hindi is 0.5 and the probability of passing neither is 0.1. If the probability of passing the English examination is 0.75, what is the probability of passing the Hindi examination?

Q21 :

In a class of 60 students, 30 opted for NCC, 32 opted for NSS and 24 opted for both NCC and NSS. If one of these students is selected at random, find the probability that

(i) The student opted for NCC or NSS.

(ii) The student has opted neither NCC nor NSS.

(iii) The student has opted NSS but not NCC.

### Exercise Miscellaneous : Solutions of Questions on Page Number : 408

Q1 :

A box contains 10 red marbles, 20 blue marbles and 30 green marbles. 5 marbles are drawn from the box, what is the probability that

(i) all will be blue? (ii) atleast one will be green?

Q2 :

4 cards are drawn from a well-shuffled deck of 52 cards. What is the probability of obtaining 3 diamonds and one spade?

Q3 :

4 cards are drawn from a well-shuffled deck of 52 cards. What is the probability of obtaining 3 diamonds and one spade?

Q4 :

A die has two faces each with number ‘1’, three faces each with number ‘2’ and one face with number ‘3’. If die is rolled once, determine

(i) P(2) (ii) P(1 or 3) (iii) P(not 3)

Q5 :

In a certain lottery, 10,000 tickets are sold and ten equal prizes are awarded. What is the probability of not getting a prize if you buy (a) one ticket (b) two tickets (c) 10 tickets?

Q6 :

Out of 100 students, two sections of 40 and 60 are formed. If you and your friend are among the 100 students, what is the probability that

(a) you both enter the same sections?

(b) you both enter the different sections?

Q7 :

Three letters are dictated to three persons and an envelope is addressed to each of them, the letters are inserted into the envelopes at random so that each envelope contains exactly one letter. Find the probability that at least one letter is in its proper envelope.

Q8 :

A and B are two events such that P(A) = 0.54, P(B) = 0.69 and P(A âˆ© B) = 0.35.

Q9 :

From the employees of a company, 5 persons are selected to represent them in the managing committee of the company. Particulars of five persons are as follows:

 S. No. Name Sex Age in years 1. Harish M 30 2. Rohan M 33 3. Sheetal F 46 4. Alis F 28 5. Salim M 41

A person is selected at random from this group to act as a spokesperson. What is the probability that the spokesperson will be either male or over 35 years?

Q10 :

If 4-digit numbers greater than 5,000 are randomly formed from the digits 0, 1, 3, 5, and 7, what is the probability of forming a number divisible by 5 when, (i) the digits are repeated? (ii) the repetition of digits is not allowed?

Q11 :

The number lock of a suitcase has 4 wheels, each labelled with ten digits i.e., from 0 to 9. The lock opens with a sequence of four digits with no repeats. What is the probability of a person getting the right sequence to open the suitcase?