# SSC Exam Quantitative Aptitude Study Material: A conceptual guide for Probability

SSC is well known for the recruitment of Group ‘B’ and ‘C’ posts under the Ministries/Departments in The Government of India. SSC organizes various examinations like Combined Graduate Level examination, Combine Higher Secondary Level, Stenographer and for SI/DP/CAPF, etc.

Created On: Jun 23, 2016 15:19 IST
Modified On: Jun 24, 2016 14:41 IST SSC is well known for the recruitment of Group ‘B’ and ‘C’ posts under the Ministries/Departments in The Government of India. SSC organizes various examinations like Combined Graduate Level examination, Combine Higher Secondary Level, Stenographer and for SI/DP/CAPF, etc., throughout the year having almost the same Exam Pattern. The Exam paper is comprised of basically 4 subjects.

a. General Intelligence & Reasoning

b. English language & Comprehension

c. Quantitative Aptitude

d. General knowledge

For more detail, click the link given below.

SSC SI, CAPF & ASI Exam 2015: Exam Pattern

SSC Combined Higher Secondary Level (10+2) Exam 2014: Exam Pattern

SSC JHT & Hindi Pradhyapak and Sr. / Jr. Translators Exam 2014: Exam Scheme & Syllabus

SSC Stenographer 2016: Take a look of Exam Pattern, Syllabus and Selection Procedure

So, Jagranjosh.com has introduced a brief plan for revising topics at the time of examination. In this article, Probability which sometimes appear more difficult to understand in terms of possibility of occurring events favorable or Unfavorable.

Probability

The mathematical measure of the uncertainty is called probability. For example, consider the following questions:

(a) Will it rain today?

(b) Which of the three candidates will win?

(c) On throwing a dice, the number obtained will be even or odd?

(d) On tossing a coin, head will occur or tail will occur?

The answer to all these question is not sure i.e. there is uncertainty .We study the uncertainty of the result of such question in the theory of probability , which may not have one result but more than one result are possible .

Random experiment:

The experiments in which the outcomes cannot be predicted before hand is called random experiments. When these kind of experiment are repeated under identical condition, they do not produce the same outcome every time and there may be many possible outcome which depends upon chance and cannot be predicted. For example, on tossing a coin either the head will come up or the tail will come up, we cannot predict it. This is an example of random event.

In term of probability if A and B are mutually exclusive events, then

P (AUB) = P (A) + P (B) and,

P (S) = P (A) + P (A’) = 1 where A’ is Complement of A.

Example: If a dice is thrown once then the probability of the number appearing on dice is more than 2?

(a) 1/3

(b) 1/2

(c) 2/3

(d) 4.3/4

Solution: As there are 6 faces on a dice,

So the total number of possible events are 1, 2 , 3 ……. 6 , that is = 6

Now the number more than are 3, 4 , 5 and 6

So total number of favourable events =

Example : An urn contains 3 green, 6 red, and 4 black balls. 3 balls are drawn. Find the probability that all 3 balls are of same colour?

(a) 3/44

(b) 25/286

(c) 15/286

(d) 5/286

Example: A bag contains 13 white and 7 black balls. Two balls are drawn at random. What is the probability that they are of the same colour?

Ans: (4)

Directions: Study the given information carefully to answer the questions that follow. An urn contains 4 green, 5 blue, 2 red and 3 yellow marbles.

Example: If two marbles are drawn at random, what is the probability that both are red or at least one is red?

Example: - If three marbles are drawn at random, what is the probability that at least one is yellow?

Ans: (3)

Example: -If eight marbles are drawn at random, what is the probability that there are equal numbers of marbles of each colour?

Solution: Total number of possible outcomes

Now, according tot the question, no marble should be green.

Total number of favourable outcomes

= Selection of 3 marbles out of 5 blue, 2 red and 3 yellow marbles

Ans: (5)

Example: - If three marbles are drawn at random, what is the probability that two are blue and two are red?

Ans: (1)

Directions: Study the given information carefully and answer the questions that follow:

A basket contains 4 red, 5 blue and 3 green marbles.

Example: - If three marbles are picked at random, what is the probability that either all are green or all are red?

Ans: (4)

Example: - If two marbles are drawn at random, what is the probability that both are red?

Ans: (5)

Example: - If three marbles are picked at random, what is the probability that at least one is blue?

Ans: (2)

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