Black and White Balls

[harsh.champ]

Two balls are to be picked at random from a drawer containing only black and white balls. What is the probability that both are white?

1. The probability of the first ball being black is 1/3.
2. There are 24 white balls in the drawer.

[gauravra025]

1- Doesnot talk about the probability of selecting next ball - Not Sufficient
2. Total Number of Balls are not mentioned - NOt Sufficient

Even if you combine both we are not aware of total number of balls. So both statements together are insufficient

[thephoenix]

Two balls are to be picked at random from a drawer containing only black and white balls. What is the probability that both are white?

1. The probability of the first ball being black is 1/3.
2. There are 24 white balls in the drawer.

IMO E

s1) we dont know bth no. of black balls and total balls
hence insuff

s2)we dnt know no. of total ball
insuff

s1+s2=insuff
for same reasons

[Ian Stewart]

Two balls are to be picked at random from a drawer containing only black and white balls. What is the probability that both are white?

1. The probability of the first ball being black is 1/3.
2. There are 24 white balls in the drawer.

The first Statement is insufficient; we may have 1 black ball and 2 white, or 10 black and 20 white - the probability of picking two white balls will be different. Statement 2 is clearly insufficient.

Combined, note that Statement 1 just gives us the ratio of white balls to black balls; we have 1 black ball for every 2 white balls. So if there are 24 white balls, there must be 12 black balls, and we can therefore answer any question about the probability of making a certain type of selection. The answer is C.

[shashank.ism]

Two balls are to be picked at random from a drawer containing only black and white balls. What is the probability that both are white?

1. The probability of the first ball being black is 1/3.
2. There are 24 white balls in the drawer.

Drawer contains only black and white balls..
St. 1 ) The probability of the first ball being black is 1/3. so probability 1st ball being white is 2/3.we don't know about the probability of 2nd ball also we don't know total no. of balls..............insuff.
St.2)total no. of balls 24 ...but how much black or white is not known . ..........so insuff....

combined since..probability of the first ball being black is 1/3. so probability 1st ball being white is 2/3. so drawer contains 24/3 = 8 black balls and 2/3 x24 = 16 white balls

now we can easily calculate the probability of both ball being white... Ans C