one probability question

[brindha_arun]

There are two identical bottles. One bottle contains 2 green balls and 1 red ball. The other contains 2 red balls. A bottle is selected at random and a single ball is drawn. What is the probability that the ball is red?

answer:!/2
1/6
2/3
1/3

I will post the right answers after the responses

[ish]

its D

[brindha_arun]

Hi ish!
You rock!
I follow almost all thy posts!
congrats on thy Bow wow wow yippee yo yippee yay!!!!11 score!

the answer is not d !
Its 2/3

Actually iam also perplexed how its 2/3

Originally Posted by ish

its D

[ish]

Thanks Brinda
oops sorry.i meant 2/3. i saw that it was the last but one choice and put in D.
this is how its 2/3


There are two identical bottles. One bottle contains 2 green balls and 1 red ball. The other contains 2 red balls. A bottle is selected at random and a single ball is drawn. What is the probability that the ball is red?

you can choose a red ball by choosing the first bottle OR the second one. The prob for choosing a bottle is 1/2. Say we choose the first one.
choosing a red ball from that one is 1/3, so the total prob for the first bottle is (1/2)(1/3)
suppose I choose the second bottle. Prob for doin that is 1/2 as well. Choosing a red one from the second one is done in 2/2 ways. Total prob is (1/2)(2/2)
Add them up, 1/6 + 1/2 is 2/3.

[samy_dg]

Required probability
=(Probability that 1st bottle is chosen & ball is red)+(Probability that 2nd bottle is chosen & ball is red)
=(1/2)X(1/3)+(1/2)X(1)
=2/3.

[brindha_arun]

WOW!
great expln. thanks try out this one


If a three digit number is formed from the digits
1,2,3,4,5,6, and 7,with no repetitions, tell how manyof these three digit numbers will have a number value between 100 and 500.

my answer is 120
pl verify my anwer

Originally Posted by samy_dg

Required probability
=(Probability that 1st bottle is chosen & ball is red)+(Probability that 2nd bottle is chosen & ball is red)
=(1/2)X(1/3)+(1/2)X(1)
=2/3.

[ish]

I got 120 as well. This is a good Q.

[brindha_arun]

Hi ish,

I am really pushing myself hard in math. Being a life science graduate, I feel the difficulty in math esply in stats, probability, A.p , g,p .
can u give me some suggestions to improve my skills in these. suggestion of any materials or websites or any posts would also be Bow wow wow yippee yo yippee yay!!!!11.

brindha

Originally Posted by ish

I got 120 as well. This is a good Q.

[ish]

There are a LOT of probability and stats sums in the GMAT PS section in TM. Visit that everytime you log in to TM.
Work on the PP math review for some stats sums. Its a good indicator for stats.
if you have time on your hands, become a member at number2.com and work on their tutorials. its a good service.
i dont have many links for math, most of them are for verbal.check our yahoo mailbox, i saw some Quants files there that may help you.
good luck
and work on your speed. you should be fast.

[brindha_arun]

The probability is 1/2 that a certain coin will turn up heads on any given toss. If the coin is to be tossed three times, what is the probability that on at least one of the tosses the coin will turn up heads?

Originally Posted by brindha_arun

There are two identical bottles. One bottle contains 2 green balls and 1 red ball. The other contains 2 red balls. A bottle is selected at random and a single ball is drawn. What is the probability that the ball is red?

answer:!/2
1/6
2/3
1/3

I will post the right answers after the responses