GateAI
Probability and Statistics

GATE CSE 2023 · Q53

MSQ2 marksEasy

Time

Consider a random experiment where two fair coins are tossed. Let AA be the event that denotes HEAD on both the throws, BB be the event that denotes HEAD on the first throw, and CC be the event that denotes HEAD on the second throw. Which of the following statements is/are TRUE?

Select all that applyOne or more correct

Pick every correct option

Solution

Step-by-step verified solution

Official answer: C) B and C are independent.; D) Prob(B|C) = Prob(B)

Probability and Statistics

Let the sample space for tossing two fair coins be:

S={HH,HT,TH,TT}S = \{HH, HT, TH, TT\}

with each elementary outcome having a probability of 14\frac{1}{4}.

The events are defined as follows:

  • Event AA (HEAD on both throws): A={HH}  ⟹  P(A)=14A = \{HH\} \implies P(A) = \frac{1}{4}

  • Event BB (HEAD on the first throw): B={HH,HT}  ⟹  P(B)=24=12B = \{HH, HT\} \implies P(B) = \frac{2}{4} = \frac{1}{2}

  • Event CC (HEAD on the second throw): C={HH,TH}  ⟹  P(C)=24=12C = \{HH, TH\} \implies P(C) = \frac{2}{4} = \frac{1}{2}

Now we test each statement:

  1. Option A: AA and BB are independent.

    A∩B={HH}  ⟹  P(A∩B)=14A \cap B = \{HH\} \implies P(A \cap B) = \frac{1}{4}
    P(A)⋅P(B)=14×12=18≠P(A∩B)P(A) \cdot P(B) = \frac{1}{4} \times \frac{1}{2} = \frac{1}{8} \neq P(A \cap B)

    Hence, AA and BB are not independent. Option A is FALSE.

  2. Option B: AA and CC are independent.

    A∩C={HH}  ⟹  P(A∩C)=14A \cap C = \{HH\} \implies P(A \cap C) = \frac{1}{4}
    P(A)⋅P(C)=14×12=18≠P(A∩C)P(A) \cdot P(C) = \frac{1}{4} \times \frac{1}{2} = \frac{1}{8} \neq P(A \cap C)

    Hence, AA and CC are not independent. Option B is FALSE.

  3. Option C: BB and CC are independent.

    B∩C={HH}  ⟹  P(B∩C)=14B \cap C = \{HH\} \implies P(B \cap C) = \frac{1}{4}
    P(B)⋅P(C)=12×12=14=P(B∩C)P(B) \cdot P(C) = \frac{1}{2} \times \frac{1}{2} = \frac{1}{4} = P(B \cap C)

    Hence, BB and CC are independent. Option C is TRUE.

  4. Option D: Prob(B∣C)=Prob(B)\text{Prob}(B|C) = \text{Prob}(B).

    Prob(B∣C)=P(B∩C)P(C)=1/41/2=12=Prob(B)\text{Prob}(B|C) = \frac{P(B \cap C)}{P(C)} = \frac{1/4}{1/2} = \frac{1}{2} = \text{Prob}(B)

    This is also an immediate property of independent events BB and CC. Option D is TRUE.

Thus, statements C and D are correct.

Try the question first, then check your work.

Think the official key or this write-up is wrong?

Report error or challenge

Examiner trap

The misconception this question tests

This Probability and Statistics previous year question is Q53 of the GATE CSE 2023 paper. Find more GATE CSE PYQs on Probability and Statistics in Engineering Mathematics, or browse all GATE CSE PYQs.

Free diagnostic

Where do you stand for GATE?

Take the 20-minute diagnostic: the 3 topics that cost you the most marks, and a rank range. Or sit 5 related Probability and Statistics PYQs now with no account.

One GATE CSE PYQ every morning

An official question by email at 7 AM IST, with a link to its verified solution. Unsubscribe in one click.

Probability and Statistics in GATE CSE

Probability and Statistics has 46 GATE CSE PYQs across 23 papers from 2011 to 2026. This is the only 2-mark MSQ among them, and it is the only one in GATE CSE 2023.

How GATE tests Probability and Statistics

More from GATE CSE 2023

Share this solution

A plain-text card for WhatsApp or Telegram study groups.

GateAI solution cardGATE CSE 2023 · Q53 · MSQ

Consider a random experiment where two fair coins are tossed. Let A be the event that denotes HEAD on both the throws, B be the event that denotes HEAD on the first throw, and C be the event that denotes HEAD on the second throw. Which of the following statements is/are TRUE?

Topic-wise GATE CS PYQs with verified steps

Independent practice explanation verified by the GateAI team. GATE is conducted by the IITs; question text follows the official paper.