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
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
(2)

Ismail said:   3 months ago
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
(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.
(6)

Asmi said:   11 months ago
At most means not 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.
(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.