Coin flip

[isvas]

DS:

Susan flipped a fair coin N times. What fraction of the flips came up heads?
(1) N = 24
(2) The number of flips that came up tails was N .

[spoiler]OA - B
To determine the fraction of the flips that came up heads, we would normally need to know the number of heads and the number of flips. Statement (1) gives us only part of the picture, the number of flips ( N ), so it is insufficient. Eliminate (A) and (D).

Statement (2) tells us the number of flips that came up tails, as a fraction of N. The only other option besides tails is heads, so we know the fraction of flips that came up heads. The value of N is then irrelevant. Statement (2) is sufficient[/spoiler]

How would I calculate the fraction?

[mohit11]

Formula = P = Fav no of cases (F)/ Total no of cases (N).


1) N - 24 , P = F/N = F/24 ..insuff.


2) Number of heads = N - Number of tails. -- N-N = 0
In other words.. if you flip a coin (say) 2 Times and you get Tail both the times, so you did not get Head even a single time.

Hence B is the answer

[isvas]

My bad, (2) should have been (3/8)N
Not N

If Tails is (3/8)N, now would you determine Heads?

[harsh.champ]

Important point over here is that you do not suffer from statement carryover when gng frm statement 1 to statement 2.
Otherwise the answer can be marked "C".

[isvas]

I still didnt get it
if Tails is (3/8)N, how can I determine Heads

OA is B - so I should not carry over (1)

[mohit11]

If no of Tails is 3/8N

Then Number of heads = N - 3/8 N

Hence B is sufficient.

[isvas]

gosh.. I missed the Q "fraction of"....
thats 5/8th of N

SILLY mistake

thanks guys