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Quantitative Aptitude

PROBABILITY MCQs

Probability, Probability I

Total Questions : 775 | Page 7 of 78 pages
Question 61. A jar contains 24 marbles, some are green and others are blue. If a marble is drawn at random from the jar, the probability that it is green is 23. Find the number of blue marbles in the jar.
  1.    12
  2.    16
  3.    11
  4.    8
 Discuss Question
Answer: Option D. -> 8
:
D
Given: P(green marble)=23
Since there are 24 marbles, therefore the sample space will be 24 (i.e. the denominator must be 24.)
Let us assume there arexnumberofgreen marbles in the jar.
For an event E, probabilityP(E)=Number of outcomes favorable to ENumber of all possible outcomes of the experiment
P(green marbles)=23=x24
x=16
It implies that there are 16 green marbles in a jar of 24 marbles.
Numberofblue marbles=2416=8.
Question 62. If an unbiased die is thrown 5 times and every throw resulted in a 6 , what is the probability of getting a 6 on the sixth throw?
  1.    less than 16
  2.    16
  3.    In between 16 to 1
  4.    1
 Discuss Question
Answer: Option D. -> 1
:
D
Total number of trials = 5
Number of trials which resulted in'6' = 5
Experimental Probability, P(E)
=Number of trials in which the event happenedTotal number of trials
=55
=1
Question 63. What is the probability of getting a sum of 13 when rolling a pair of dice?
  1.    0
  2.    113
  3.    112
  4.    111
 Discuss Question
Answer: Option A. -> 0
:
A
The highest sum possible when rolling a pair of dice is 12(getting 6 on both dies). So getting a sum of 13 is an impossible event. Hence, the probability is 0.
Question 64.  Indians , Egyptians , Europeans and Australians are residing in a village of area 200 km2. If the area is equally divided between the four countries, what is the probability that a particular person who lands in the village, finds himself in the area occupied by either Indians or Europeans? 
  1.    0.60
  2.    0.33
  3.    0.45
  4.    0.50
 Discuss Question
Answer: Option D. -> 0.50
:
D
Each countryoccupies an area of 50km2
Probability that the person lands on a land occupied by Indians or Europeans = (50+50)200 = 12 = 0.50
Question 65. The probability of picking the letter K if you pick a random letter from the word TREKKING is x4. x is 
___
 Discuss Question

:
The word TREKKING has 8 characters of which 2 are favourable. Hence, the probability is 28= 14.
Question 66. The sum of probabilities of two mutually exclusive events will always be 1.
  1.    True
  2.    False
 Discuss Question
Answer: Option B. -> False
:
B
The sum of probabilities of two mutually exclusive events need not be always1.
For example, consider the events “getting a prime number”, and “getting a composite number” for the experiment ofrolling a die. They are mutually exclusive, but the sum of their probabilities is less than 1.
Favorable outcomes for prime no. = 2 , 3, 5
Favorable outcomes for composite no. = 4, 6
P(getting a prime no.) =36=12
P(getting a composite no.) =26=13
12+131. SoThe sum of probabilities of two mutually exclusive events need not be always1.
Question 67. 5 defective glasses are accidentally mixed with 20 good ones. The good glasses and the defective ones look the same from the outside. If a glass is chosen at random, what is the probability that the chosen glass is good?
  1.    38
  2.    45
  3.    35
  4.    25
 Discuss Question
Answer: Option B. -> 45
:
B
Given, total number of glasses =25(20+5)
⇒ Total number of outcomes =25
Let E be the event of getting good glass.
Number ofgood ones =20
⇒ Number of favourable outcomes =20
Probability P(E)=Number of outcomes favourable to ENumber of all possible outcomes of the experiment
=2025=45
The probability of getting a good glass is 45.
Question 68. What is the probability of getting a sum of 7 on two rolls of a die?
  1.    712
  2.    111
  3.    16
  4.    23
 Discuss Question
Answer: Option C. -> 16
:
C
The total possible outcomes when a die is rolled twice are:
12345611,11,21,31,41,51,622,12,22,32,42,52,633,13,23,33,43,53,644,14,24,34,44,54,655,15,25,35,45,55,666,16,26,36,46,56,6
Total number of outcomes = 36
Number of ways to get sum as 7= {(1,6), (2,5), (3,4), (4,3), (5,2), (6,1)}
= 6
P(getting sum as 7)=Favourable outcomesTotal possible outcomes
=OutcomehavingsamenumbersTotalOutcomes
=636
=16
Question 69. A card is drawn at random from a well-shuffled deck of 52 cards.What is the probability that the card drawn is a diamond?
  1.    12
  2.    13
  3.    14
  4.    15
 Discuss Question
Answer: Option C. -> 14
:
C
Given,
Total number of outcomes = 52
Number of diamonds = 13
Probability of an event, P(E) = =number of favourable outcomestotal number of outcomes
P (getting a card of diamond) = 1352=14
Therefore, probability of getting a card of diamond is 14 .
Question 70. The set of all possible outcomes associated with an experiment is called as________.
  1.    outcomes
  2.    sample space
  3.    trials
  4.    None of the above
 Discuss Question
Answer: Option B. -> sample space
:
B
In probability theory, the sample space of an experiment or random trial is the set of all possible outcomes or results of that experiment.
For example, if we toss a single coin then the chances are that either head willappear or tail will appear,the sample space will be {H}, {T}.

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