GateAI
Probability and Statistics

GATE CSE 2016 Set 1 · Q29

NAT2 marksEasy

Time

Consider the following experiment. Step 1. Flip a fair coin twice. Step 2. If the outcomes are (TAILS, HEADS) then output YY and stop. Step 3. If the outcomes are either (HEADS, HEADS) or (HEADS, TAILS), then output NN and stop. Step 4. If the outcomes are (TAILS, TAILS), then go to Step 1. The probability that the output of the experiment is YY is (up to two decimal places) ________ .

Your answerNumerical answer

Enter a value to check

Solution

Step-by-step verified solution

Official answer: 0.33 (±0.01) (±0.01)

Probability and Statistics

When a fair coin is flipped twice, there are 4 equally likely outcomes, each with probability 14\frac{1}{4}:

  1. (TAILS,HEADS)(\text{TAILS}, \text{HEADS}) with probability 14  ⟹  \frac{1}{4} \implies Output YY and stop.

  2. (HEADS,HEADS)(\text{HEADS}, \text{HEADS}) or (HEADS,TAILS)(\text{HEADS}, \text{TAILS}) with total probability 24=12  ⟹  \frac{2}{4} = \frac{1}{2} \implies Output NN and stop.

  3. (TAILS,TAILS)(\text{TAILS}, \text{TAILS}) with probability 14  ⟹  \frac{1}{4} \implies Repeat Step 1.

Let P(Y)P(Y) be the probability that the experiment eventually outputs YY. By the law of total probability:

P(Y)=14+14P(Y)P(Y) = \frac{1}{4} + \frac{1}{4} P(Y)

Solving for $P(Y)$:

P(Y)−14P(Y)=14P(Y) - \frac{1}{4} P(Y) = \frac{1}{4}
34P(Y)=14\frac{3}{4} P(Y) = \frac{1}{4}
P(Y)=13≈0.33P(Y) = \frac{1}{3} \approx 0.33

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 Q29 of the GATE CSE 2016 Set 1 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. 15 of them are 2-mark NAT questions like this one, and GATE CSE 2016 Set 1 has 2.

How GATE tests Probability and Statistics

More from GATE CSE 2016 Set 1

Share this solution

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

GateAI solution cardGATE CSE 2016 Set 1 · Q29 · NAT

Consider the following experiment. Step 1. Flip a fair coin twice. Step 2. If the outcomes are (TAILS, HEADS) then output Y and stop. Step 3. If the outcomes are either (HEADS, HEADS) or (HEADS, TAILS), then output N and stop. Step 4. If the outcomes are (TAILS, TAILS), then go to Step 1. The probability that the output of the experiment is Y is (up to two decimal places) …

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.