souvonik2k wrote:

Two players are to be selected from a football team which consists of 10 football players. Is the probability that both the players chosen will be left backs greater than 50 %?

(1) The probability that both players selected will not be left backs is less than 10 %

(2) More than fifty percent of the players are left backs.

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Hi...

A good Q..

So we have to choose 2 out of 10.

(1) The probability that both players selected will not be left backs is less than 10 %

Let there be x non left backs, so prob of choosing both is \(\frac{x}{10}*\frac{x-1}{10}<\frac{10}{100}\)...

So x(x-1)<10....

x =3 or <3 because 4*3=12>10 and 3*2=6<10...

So if x=3, left backs are 10-3=7

Prob =7/10*6/9=42/90<50%

If x=2, prob =8/10*7/9=56/90>50%

So insuff

(2) More than fifty percent of the players are left backs.

Say there are 6 or 7, as seen above itwill be <50%

And above 8,9 or 10, prob will be >50%

Insufficient

Combined..

If it is 7, Ans is NO

If 8,9 or 10, Ans is YES

Insufficient

E

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Absolute modulus :http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372

Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html