A jar contains 8 red marbles and y white marbles. If Joan takes 2 random marbles from the jar, is it more likely that she will have 2 red marbles than that she will have one marble of each color?
(1) y ≤ 8
(2) y ≥ 4
Jars ratio
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- sumgb
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let's put the probability of selecting both red marbles:
{8 / (8+y)}{7/(7+y)}
probability of 1 of each color:
{8 / (8+y)}{y/(7+y)}
what you need to find out in this question is:
{8 / (8+y)}{7/(7+y)} > {8 / (8+y)}{y/(7+y)} which means
56 / {(8+y)(7+y)} > 8y / {(8+y)(7+y)} which means
56 > 8y which means
7 > y that is Is y < 7?
stmnt 1: y ≤ 8 clearly insuff; cross off A D
stmnt 2: y ≥ 4 also insuff; cross off B
together we have 4 <= y <= 8; also insuff as y could still be 8; cross off C
Answer E
What is OA and OE?
Hope this helps...
{8 / (8+y)}{7/(7+y)}
probability of 1 of each color:
{8 / (8+y)}{y/(7+y)}
what you need to find out in this question is:
{8 / (8+y)}{7/(7+y)} > {8 / (8+y)}{y/(7+y)} which means
56 / {(8+y)(7+y)} > 8y / {(8+y)(7+y)} which means
56 > 8y which means
7 > y that is Is y < 7?
stmnt 1: y ≤ 8 clearly insuff; cross off A D
stmnt 2: y ≥ 4 also insuff; cross off B
together we have 4 <= y <= 8; also insuff as y could still be 8; cross off C
Answer E
What is OA and OE?
Hope this helps...
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Let total number of possible ways of selecting any 2 marbles be 'S'.
probability of selecting 2 red marbles=8C2/S=28/S. ......(i)
probability of selecting 1 red and 1 white marble=8C1*YC1/S. ...... (ii)
Now if Y>=4 then YC1=4C1=4 which will render (ii) greater than (i).
Statement (1): Y<=8 . No sufficient as Y can be 2 or 8
Statement (2): Y>=4 . Sufficient as Y is >=4
probability of selecting 2 red marbles=8C2/S=28/S. ......(i)
probability of selecting 1 red and 1 white marble=8C1*YC1/S. ...... (ii)
Now if Y>=4 then YC1=4C1=4 which will render (ii) greater than (i).
Statement (1): Y<=8 . No sufficient as Y can be 2 or 8
Statement (2): Y>=4 . Sufficient as Y is >=4
Last edited by beatthegmat.garry on Mon Aug 15, 2011 10:09 pm, edited 1 time in total.
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Hi,beatthegmat.garry wrote:Let total number of possible ways of selecting any 2 marbles be 'S'.
probability of selecting 2 red marbles=8C2/S=28/S. ......(i)
probability of selecting 1 red and 1 white marble=8C1*YC1/S. ...... (ii)
Now if Y>=3 then YC1=3C1=3 which will render (ii) greater than (i).
Statement (1): Y<=8 . No sufficient as Y can be 2 or 8
Statement (2): Y>=4 . Sufficient as Y is >=3
Almost correct but minor error. For y=3, (ii) is not greater than (i)
For y>=4, (ii) > (i)
Is 28/S > 8y/S? => Is y<7/2
So, if y<=3, the answer is yes
if y>=4, answer is No.
statement(2) is sufficient
Hence, B
Cheers!
Things are not what they appear to be... nor are they otherwise
Things are not what they appear to be... nor are they otherwise
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- sumgb
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Yes indeed.
2{8 / (8+y)}{y/(7+y)}
so is y < 3.5
clearly stmnt 2 is the winner.
Thanks guys...
This is wrong.let's put the probability of selecting both red marbles:
{8 / (8+y)}{7/(7+y)}
probability of 1 of each color:
{8 / (8+y)}{y/(7+y)}
what you need to find out in this question is:
{8 / (8+y)}{7/(7+y)} > {8 / (8+y)}{y/(7+y)} which means
56 / {(8+y)(7+y)} > 8y / {(8+y)(7+y)} which means
56 > 8y which means
7 > y that is Is y < 7?
this should be -probability of 1 of each color:
{8 / (8+y)}{y/(7+y)}
2{8 / (8+y)}{y/(7+y)}
so is y < 3.5
clearly stmnt 2 is the winner.
Thanks guys...