# Aptitude - Probability - Discussion

Discussion Forum : Probability - General Questions (Q.No. 5)

5.

Three unbiased coins are tossed. What is the probability of getting at most two heads?

Answer: Option

Explanation:

Here S = {TTT, TTH, THT, HTT, THH, HTH, HHT, HHH}

Let E = event of getting at most two heads.

Then E = {TTT, TTH, THT, HTT, THH, HTH, HHT}.

P(E) = | n(E) |
= | 7 | . |

n(S) |
8 |

Discussion:

119 comments Page 1 of 12.
Reena said:
3 months ago

At most 2 heads means it cannot be more than 2. It can be zero or 1 or 2 but not 3. And there is only one case that have 3 (HHH). So probability is 7/8.

(5)

Ragini said:
3 months ago

The right Answer is 3/8.

(2)

Ismail said:
3 months ago

"At most 2 head" means a maximum 2 no. of heads that is there can be 0 heads,1 head or 2 heads.

So, TTT, TTH, THT, THH, HTT, HHT, HTH have at most 2 heads.

So, n(E)=7 & n(S)= 8 ---> n(E)/n(S) = 7/8.

So, TTT, TTH, THT, THH, HTT, HHT, HTH have at most 2 heads.

So, n(E)=7 & n(S)= 8 ---> n(E)/n(S) = 7/8.

(1)

Sowmya said:
4 months ago

The Answer should be 3/8.

(2)

Manisha Yadav said:
8 months ago

The right answer should be 3/8.

(14)

Chelsia said:
8 months ago

We can get quickly the number of events like 2 to the Power of (number of coins).

I.e 2'3=> 8.

I.e 2'3=> 8.

(6)

Asmi said:
11 months ago

At most means not more than 2 heads.

And at least means more than 2 heads.

And at least means more than 2 heads.

(20)

Jiju said:
1 year ago

At most means maximum, that means no more than 2 heads, so the events include TTT, HTT, HHT, THH, TTH, HTH, and THT.

HHH is not right because it's more than two heads, at most means not more than two so it includes 0 heads, 1 head, 2 heads.

HHH is not right because it's more than two heads, at most means not more than two so it includes 0 heads, 1 head, 2 heads.

(39)

Shobha said:
1 year ago

I don't understand this logic - Then E = {TTT, TTH, THT, HTT, THH, HTH, HHT}.

As this question says event of getting at most two heads.

It should be these combinations- THH, HTH, HHT, HHH.

Please, someone, explain.

As this question says event of getting at most two heads.

It should be these combinations- THH, HTH, HHT, HHH.

Please, someone, explain.

(15)

Triveni said:
1 year ago

I can't Understand this. Anyone, please help me to get this.

(1)

Post your comments here:

Quick links

Quantitative Aptitude

Verbal (English)

Reasoning

Programming

Interview

Placement Papers