For each 6-month period during a light bulb's life span, the odds of it not burning out from over-use are half what they were in the previous 6-month period. If the odds of a light bulb burning out during the first 6-month period following its purchase are 1/3, what are the odds of it burning out during the period from 6 months to 1 year following its purchase?
5/27
2/9
1/3
4/9
2/3
probability question
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p(no burn now) = 1/2 * p(no burn in the previous 6-month period)rishianand7 wrote:For each 6-month period during a light bulb's life span, the odds of it not burning out from over-use are half what they were in the previous 6-month period. If the odds of a light bulb burning out during the first 6-month period following its purchase are 1/3, what are the odds of it burning out during the period from 6 months to 1 year following its purchase?
5/27
2/9
1/3
4/9
2/3
1-p(burning out now) = 1/2 * (1 - p(burning out in the first six months))
1 - P = 1/2 * (1 - 1/3)
1 - P = 1/2 * 2/3
1 - P = 1/3
P = 2/3
Choose E
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I'm not too crazy about the wording of this question, since there's a big difference between ODDS and PROBABILITYrishianand7 wrote:For each 6-month period during a light bulb's life span, the odds of it not burning out from over-use are half what they were in the previous 6-month period. If the odds of a light bulb burning out during the first 6-month period following its purchase are 1/3, what are the odds of it burning out during the period from 6 months to 1 year following its purchase?
5/27
2/9
1/3
4/9
2/3
Probability = (favorable outcomes)/ (total outcomes)
Odds = the ratio of favorable outcomes to unfavorable outcomes
So, for example, if we randomly select a number from {3, 5, 7, 9, 11}, then . . .
- The PROBABILITY of selecting a prime number = 4/5
- The ODDS in favor of selecting a prime number = 4:1
I don't think I've ever seen the GMAT use the term "odds" (other than in the context of even and odd integers).
Having said all of that, if we take the question and replace "odds" with "probability" then ganeshrkamath's solution is perfect (as always )
Cheers,
Brent
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Thanks Brent.Brent@GMATPrepNow wrote:I'm not too crazy about the wording of this question, since there's a big difference between ODDS and PROBABILITYrishianand7 wrote:For each 6-month period during a light bulb's life span, the odds of it not burning out from over-use are half what they were in the previous 6-month period. If the odds of a light bulb burning out during the first 6-month period following its purchase are 1/3, what are the odds of it burning out during the period from 6 months to 1 year following its purchase?
5/27
2/9
1/3
4/9
2/3
Probability = (favorable outcomes)/ (total outcomes)
Odds = the ratio of favorable outcomes to unfavorable outcomes
So, for example, if we randomly select a number from {3, 5, 7, 9, 11}, then . . .
- The PROBABILITY of selecting a prime number = 4/5
- The ODDS in favor of selecting a prime number = 4:1
I don't think I've ever seen the GMAT use the term "odds" (other than in the context of even and odd integers).
Having said all of that, if we take the question and replace "odds" with "probability" then ganeshrkamath's solution is perfect (as always )
Cheers,
Brent
Taking your definition of odds,
Odds of a light bulb burning out during the first 6 month period = 1/3
Odds of a light bulb NOT burning out during the first 6 month period = 3/1
Odds of a light bulb NOT burning out during the next 6 month period = 3/2
Odds of a light bulb burning out during the next 6 month period = 2/3
The answer is still the same: E
Cheers
Every job is a self-portrait of the person who did it. Autograph your work with excellence.
Kelley School of Business (Class of 2016)
GMAT Score: 750 V40 Q51 AWA 5 IR 8
https://www.beatthegmat.com/first-attemp ... tml#688494
Kelley School of Business (Class of 2016)
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https://www.beatthegmat.com/first-attemp ... tml#688494
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Good point, ganeshrkamath, but I think that might be a coincidence resulting from the numbers used in the question.ganeshrkamath wrote:
Taking your definition of odds,
Odds of a light bulb burning out during the first 6 month period = 1/3
Odds of a light bulb NOT burning out during the first 6 month period = 3/1
Odds of a light bulb NOT burning out during the next 6 month period = 3/2
Odds of a light bulb burning out during the next 6 month period = 2/3
The answer is still the same: E
Cheers
For example, if the question had asked for the chances of the light bulb burning out during the period from 1 year to 18 months following its purchase, then the ODDS would be 4:3, but the PROBABILITY would be 5/6
That said, my main point is that the GMAT will not ask us to determine the odds of an event occurring.
Cheers,
Brent
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Here's the explanation from Kaplan.
"If the odds of a light bulb burning out in the first six months are , then will still be functional after 6 months. Now, if the chance of a light bulb NOT burning out is halved after this first 6-month period, then the odds of it burning out are simultaneously doubled. So the odds that a light bulb which survived the first 6 months will burn out in the period from 6 months to 1 year are no longer , but . You now have that of the light bulbs survive to the 6-month to 1-year period, and that of these will burn out during this time. Multiplying by , you find that the odds of a light bulb burning out during the period from 6 months to 1 year following its purchase are . (D) is correct."
Safe to say this won't be on the GMAT?
"If the odds of a light bulb burning out in the first six months are , then will still be functional after 6 months. Now, if the chance of a light bulb NOT burning out is halved after this first 6-month period, then the odds of it burning out are simultaneously doubled. So the odds that a light bulb which survived the first 6 months will burn out in the period from 6 months to 1 year are no longer , but . You now have that of the light bulbs survive to the 6-month to 1-year period, and that of these will burn out during this time. Multiplying by , you find that the odds of a light bulb burning out during the period from 6 months to 1 year following its purchase are . (D) is correct."
Safe to say this won't be on the GMAT?
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It's safe to say that you won't be asked to find ODDS.sdotgarcia wrote: Safe to say this won't be on the GMAT?
Cheers,
Brent