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saafiin
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Probability...

by saafiin Sat Nov 19, 2011 2:10 pm

Q: In a certain bag there are 12 identical blue balls, y identical yellow balls and no other ball. One ball will randomly removed. If the probability is less than 2/3 that the removed ball will be blue, then what is the least number of yellow balls that must be in the bag?

a. 17
b. 18
c. 19
d. 20
e. 21


please need help...unable to solve...
RonPurewal
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Re: Probability...

by RonPurewal Wed Nov 23, 2011 6:59 am

saafiin wrote:Q: In a certain bag there are 12 identical blue balls, y identical yellow balls and no other ball. One ball will randomly removed. If the probability is less than 2/3 that the removed ball will be blue, then what is the least number of balls that must be in the bag?

a. 17
b. 18
c. 19
d. 20
e. 21


please need help...unable to solve...


i changed the text to something that makes sense with the given answer choices.

the problem wants the least number, so, try out the choices starting with the smallest one.

if there are (a) 17 balls -- 12 blue and 5 yellow -- then the probability of getting a blue one is 12/17, which is greater than 2/3. no good.

if there are (b) 18 balls -- 12 blue and 6 yellow -- then the probability of getting a blue one is 12/18, which is equal to 2/3. no good.

if there are (c) 19 balls -- 12 blue and 7 yellow -- then the probability of getting a blue one is 12/19, which is less than 2/3.

done. (c)
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krishnan.anju1987
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Re: Probability...

by krishnan.anju1987 Thu Jul 05, 2012 7:56 pm

RonPurewal wrote:
saafiin wrote:Q: In a certain bag there are 12 identical blue balls, y identical yellow balls and no other ball. One ball will randomly removed. If the probability is less than 2/3 that the removed ball will be blue, then what is the least number of balls that must be in the bag?

a. 17
b. 18
c. 19
d. 20
e. 21


please need help...unable to solve...


i changed the text to something that makes sense with the given answer choices.

the problem wants the least number, so, try out the choices starting with the smallest one.

if there are (a) 17 balls -- 12 blue and 5 yellow -- then the probability of getting a blue one is 12/17, which is greater than 2/3. no good.

if there are (b) 18 balls -- 12 blue and 6 yellow -- then the probability of getting a blue one is 12/18, which is equal to 2/3. no good.

if there are (c) 19 balls -- 12 blue and 7 yellow -- then the probability of getting a blue one is 12/19, which is less than 2/3.

done. (c)


Hi Ron,

A quick question. I found out algebraically that the least number of yellow balls were 7 but was then stumped when I saw double digit numbers as the answers for the yellow balls. Looks like either I misinterpreted the question and was expecting the answer to be the number of yellow balls instead of the total balls or the question is slightly wrong.
tim
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Re: Probability...

by tim Fri Jul 06, 2012 8:39 am

yes the question is wrong. did you read Ron's post?
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krishnan.anju1987
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Re: Probability...

by krishnan.anju1987 Fri Jul 06, 2012 12:01 pm

Guess I missed it. Thanks for confirming.
jnelson0612
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Re: Probability...

by jnelson0612 Sat Jul 07, 2012 5:07 pm

:-)
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