Home › Exam notes › SSC CGL › Elementary Probability

Elementary Probability

Quantitative Aptitude · Maths Bookwise · Data & Reasoning

Useful for: SSC CGL

BOOK-GUIDED ORIGINAL SSC MATHS PRACTICE — Elementary Probability

FOUNDATION

P(event) = favourable outcomes / total equally likely outcomes.

METHOD

Identify the quantities given, choose the exact relationship, calculate in the same unit, then check the answer against the question.

WORKED EXAMPLE 1

A bag has 68 red and 102 blue balls. One is picked uniformly at random. Find the probability of red (in %).

Total outcomes = 68+102=170. P(red)=68/170=4/10. In percent = 40%.

WORKED EXAMPLE 2

A bag has 78 red and 182 blue balls. One is picked uniformly at random. Find the probability of red (in %).

Total outcomes = 78+182=260. P(red)=78/260=3/10. In percent = 30%.

IMPORTANT EXCEPTION / COMMON TRAP

Probabilities lie between 0 and 1 inclusive.

QUICK REVISION

P(event) = favourable outcomes / total equally likely outcomes.

SEE MORE: https://study.kundali-iq.com/ssc-maths/probability/

For complete timed maths practice, use SSC CGL Test Series → New Maths 100 Mixed Sets or Chapter-wise sets. These are independent original questions, not copied previous-year questions.

Practice MCQs

A bag has 68 red and 102 blue balls. One is picked uniformly at random. Find the probability of red (in %).
1. 44
2. 40
3. 42
4. 38
Read chapter notes · Similar questions
Show answer
Answer: (b) 40. Total outcomes = 68+102=170. P(red)=68/170=4/10. In percent = 40%.
A bag has 78 red and 182 blue balls. One is picked uniformly at random. Find the probability of red (in %).
1. 30
2. 32
3. 34
4. 28
Read chapter notes · Similar questions
Show answer
Answer: (a) 30. Total outcomes = 78+182=260. P(red)=78/260=3/10. In percent = 30%.
A bag has 280 red and 120 blue balls. One is picked uniformly at random. Find the probability of red (in %).
1. 66
2. 78
3. 74
4. 70
Read chapter notes · Similar questions
Show answer
Answer: (d) 70. Total outcomes = 280+120=400. P(red)=280/400=14/20. In percent = 70%.
A bag has 28 red and 7 blue balls. One is picked uniformly at random. Find the probability of red (in %).
1. 75
2. 85
3. 80
4. 90
Read chapter notes · Similar questions
Show answer
Answer: (c) 80. Total outcomes = 28+7=35. P(red)=28/35=4/5. In percent = 80%.
When two fair dice are rolled, what is the probability that their sum is 7
1. 1/9
2. 1/12
3. 1/6
4. 1/3
Read chapter notes · Similar questions
Show answer
Answer: (c) 1/6. There are 6 favourable ordered pairs out of 36 equally likely outcomes; probability = 6/36 = 1/6.

Elementary Probability

Practice MCQs

More topics in this chapter