Everything you need to ace this chapter, in one place.
Notes · Mind Map · Quiz · Assertion-Reason · Case Studies · Question Bank · Past Papers
Q1. When a die is rolled, which of the following represents a simple event?
Answer: B — A simple event contains exactly one sample point; {5} contains only the outcome 5, making it a simple event.
Q2. In tossing two coins, let A be the event 'at least one head' and B be the event 'exactly one tail'. Which statement is true?
Answer: B — A = {HH, HT, TH} and B = {HT, TH}; their intersection contains outcomes common to both, which are {HT, TH}.
Q3. If E is the event 'getting a multiple of 7 on rolling a die', then E is classified as:
Answer: C — No outcome on a die (1–6) is a multiple of 7, so E = φ, making it an impossible event.
Q4. Two events A and B are mutually exclusive if and only if:
Answer: B — Mutually exclusive events cannot occur simultaneously, which means they have no common outcomes, so A ∩ B = φ.
Q5. In rolling a die, let A = 'prime number' = {2, 3, 5} and B = 'number greater than 3' = {4, 5, 6}. What is A but not B?
Answer: A — A but not B = A − B = A ∩ B′; outcomes in A that are NOT in B are 2 and 3, so the answer is {2, 3}.
Q6. Which of the following is NOT correct about complementary events A and A′?
Answer: D — Complementary events are disjoint (A ∩ A′ = φ), not equal to the entire sample space; option D is incorrect.
Q7. In the experiment of tossing three coins, the event 'at most two heads' corresponds to which set?
Answer: D — 'At most two heads' means 0, 1, or 2 heads; this includes all 8 outcomes except HHH, giving {TTT, HTT, THT, TTH, HHT, HTH, THH}.
Q8. Assertion (A): Simple events of a sample space are always mutually exclusive. Reason (R): Each simple event contains exactly one sample point, and no two simple events share the same sample point.
Answer: A — Both statements are true: simple events contain one point each and cannot share outcomes, making them mutually exclusive; R correctly explains why A is true.
Q9. In rolling a die twice, let A = 'first roll is 6' and B = 'sum is at least 11'. How many outcomes satisfy both A and B?
Answer: B — A = {(6,1), (6,2), (6,3), (6,4), (6,5), (6,6)}, B = {(5,6), (6,5), (6,6)}; A ∩ B = {(6,5), (6,6)}, which contains 2 outcomes.
Q10. If S = {1, 2, 3, 4, 5, 6, 7, 8}, and events P = {2, 4, 6, 8} and Q = {3, 6}, then which statement is true?
Answer: D — P′ = {1, 3, 5, 7}, so P′ ∪ Q = {1, 3, 5, 7}; P ∩ Q = {6}, so (P ∩ Q)′ = {1, 2, 3, 4, 5, 7, 8}; Q′ = {1, 2, 4, 5, 7, 8}, so P ∩ Q′ = {2, 4, 8}; all three are correct.
What is an event in probability?
An event is any subset E of the sample space S associated with a random experiment.
When does an event E occur?
Event E occurs if the outcome ω of the experiment satisfies ω ∈ E.
What is a simple event?
A simple event is an event containing exactly one sample point from the sample space.
What is a compound event?
A compound event is an event containing more than one sample point from the sample space.
Define impossible and sure events.
Impossible event = φ (empty set, never occurs); Sure event = S (entire sample space, always occurs).
What does A′ (complement) represent?
A′ is the event 'not A', containing all outcomes in S that are not in A, where A′ = S − A.
When are two events mutually exclusive?
Events A and B are mutually exclusive if they cannot occur simultaneously, meaning A ∩ B = φ.
What is the difference between 'A or B' and 'A and B'?
'A or B' = A ∪ B (at least one occurs); 'A and B' = A ∩ B (both occur together).
How is 'A but not B' expressed using set notation?
'A but not B' is represented as A − B = A ∩ B′, containing outcomes in A that are not in B.
Why are simple events always mutually exclusive?
Simple events are mutually exclusive because each contains a unique single sample point, so no two simple events can share an outcome.
Define a simple event and a compound event. Give one example of each from the experiment of tossing a coin twice. [2 marks]
Simple event has exactly 1 sample point; compound event has 2+ sample points. For tossing 2 coins, use sample space S = {HH, HT, TH, TT}.
In rolling a die, let A be the event 'getting a number less than or equal to 3' and B be the event 'getting an odd number'. Find (i) A ∪ B, (ii) A ∩ B, (iii) A − B, and (iv) A′ ∩ B. Show all working steps. [5 marks]
First write A = {1, 2, 3} and B = {1, 3, 5}. Use definitions: A ∪ B includes all elements in A or B; A ∩ B is common elements; A − B = A ∩ B′; A′ = S − A then intersect with B.
Explain the concepts of mutually exclusive events and exhaustive events. Prove that if A and B are mutually exclusive and exhaustive events, then A ∪ B = S and A ∩ B = φ. Give a real-world example from the experiment of rolling a die. [6 marks]
Define mutually exclusive as A ∩ B = φ (cannot both occur) and exhaustive as A ∪ B = S (together cover all outcomes). Show both conditions hold simultaneously using set properties. Use example: A = 'even number' and B = 'odd number' on a die where A ∩ B = φ and A ∪ B = {1, 2, 3, 4, 5, 6}.
Q1. Assertion (A):
In the experiment of tossing three coins, the event 'exactly one head appears' is a compound event.
Reason (R):
A compound event is any event that contains more than one sample point.
Answer: A — Both A and R are true, and R is the correct explanation of A — The event 'exactly one head' = {HTT, THT, TTH}, which has three sample points. By definition, an event with more than one sample point is compound. The reason correctly explains why it is compound.
Q2. Assertion (A):
Two events A and B are mutually exclusive if A ∩ B = φ.
Reason (R):
Mutually exclusive events cannot occur at the same time because they share at least one common outcome.
Answer: C — A is true but R is false — The assertion is true—mutually exclusive events have no common outcomes (empty intersection). However, the reason is false; it incorrectly states they share 'at least one common outcome,' which contradicts the definition. The reason reverses the logic.
Q3. Assertion (A):
The complement of event A, denoted A', contains all outcomes in the sample space that are not in A.
Reason (R):
A' = S – A, and A ∪ A' = S while A ∩ A' = φ.
Answer: B — Both A and R are true, but R is NOT the correct explanation of A — Both the assertion and reason are true. The assertion correctly defines a complementary event. The reason provides mathematical properties of complementary events, but it does not directly explain why A' is defined as S – A; it only states consequences. Thus, the reason is true but not the direct explanation.
Unlock more Assertion-Reason questions in Premium — unlock →
Case Study:
A school conducted a survey on student participation in extracurricular activities. Out of 200 students, 120 participate in sports (S), 90 participate in cultural programs (C), and 40 participate in both. The school wants to analyze different categories of student participation. For a randomly selected student from the survey: Event A represents students who participate in sports, Event B represents students who participate in cultural programs.
Q1. What is the event 'students participating in sports but not cultural programs'?
Answer: B
Q2. How many students participate in either sports or cultural programs?
Answer: C
Q3. Which set represents students participating in neither sports nor cultural programs?
Answer: A
Q4. How many students participate in neither activity?
Answer: A
Unlock more case studies in Premium — unlock →
Every formula from all 14 chapters on one page, checked against the NCERT textbook and the CBSE 2026-27 syllabus. Free PDF download.
You've seen the free preview. Open the full interactive study kit — mind map, instant-graded quiz, progress tracking — free, no sign-in required.
Open Full Study Kit — Free →Premium unlocks the full Question Bank, Daily Practice Papers, Chapter Quiz and Full Mock Papers for every chapter.