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?
3
4
1
4
3
8
7
8
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:
120 comments Page 1 of 12.

Jiju said:   2 years 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.
(42)

Amit Verma said:   2 years ago
Here S = {TTT, TTH, THT, THH, HHH, HHT, HTH, HTT}
Let E = Even of getting at most two heads.
Then E = {HHH, HHT, HTH, THH},
P(E) = n(E)/n(S),
= 4/8 = 1/2.
(37)

Reena said:   10 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.
(26)

Asmi said:   2 years ago
At most means not more than 2 heads.

And at least means more than 2 heads.
(24)

Shobha said:   2 years 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.
(21)

Manisha Yadav said:   1 year ago
The right answer should be 3/8.
(14)

Ragini said:   10 months ago
The right Answer is 3/8.
(9)

Chelsia said:   1 year ago
We can get quickly the number of events like 2 to the Power of (number of coins).

I.e 2'3=> 8.
(7)

Ismail said:   11 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.
(7)

Meena said:   4 years ago
The question is what is the probability of getting "at most" two heads?

Here, at most two heads mean Not more than two heads.
So, HHH is more than two heads. It is not counted in Event. Am I right?
(6)


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