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If a number is drawn at random from the first 1000 positive [#permalink]
 23 Nov 2005, 07:19
Question Stats:
22% (01:02) correct
77% (03:22) wrong based on 9 sessions
If a number is drawn at random from the first 1000 positive integers, what is the probability of selecting a refined number? (1) Any refined number must be divisible by 22 (2) A refined number is any even multiple of 11
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Re: DS PGMAT (probability) [#permalink]
23 Nov 2005, 08:13
GMATT73 wrote: If a number is drawn at random from the first 1000 positive integers, what is the probability of selecting a refined number?
1. Any refined number must be divisible by 22
2. A refined number is any even multiple of 11
I think it should be D
1. you can find the number of numbers divisible by 22 and less than 1000 ----> sufficient
2. you can find the number of numbers divisible by 11 and less than 1000 ----> sufficient
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Current Student
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Sorry guys, OA is not D. Any other guesses?
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B?
Somehow I think the wordings are a little tricky.........
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Current Student
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1. Statement 1 tells us that a refined number must be a multiple of 22. This is a necessary, but not sufficient condition for a refined number. While every refined number is a multiple of 22, every multiple of 22 is not necessarily a refined number. Since we have no other info about the definition of a refined number, we cannot determine how many integers from 1-1000 fit that definition. Insuff.
2. Statement 2 provides us with a definition of a refined number- an even multiple of 11. We can find the number of even multiples of 11 in the set, so this is sufficient.
OA is (B)
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GMATT73 wrote: 1. Statement 1 tells us that a refined number must be a multiple of 22. This is a necessary, but not sufficient condition for a refined number. While every refined number is a multiple of 22, every multiple of 22 is not necessarily a refined number. Since we have no other info about the definition of a refined number, we cannot determine how many integers from 1-1000 fit that definition. Insuff.
2. Statement 2 provides us with a definition of a refined number- an even multiple of 11. We can find the number of even multiples of 11 in the set, so this is sufficient.
OA is (B)
Isn't (2) just a repetition of (1)?
(2) says the refined number must be an even multiple of 11. So a refined number can be 22, 44, 66, 88, 110,... etc... All these are multiples off 22, which is given in (1).
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GMATT73 wrote: 1. Statement 1 tells us that a refined number must be a multiple of 22. This is a necessary, but not sufficient condition for a refined number. While every refined number is a multiple of 22, every multiple of 22 is not necessarily a refined number. Since we have no other info about the definition of a refined number, we cannot determine how many integers from 1-1000 fit that definition. Insuff.
2. Statement 2 provides us with a definition of a refined number- an even multiple of 11. We can find the number of even multiples of 11 in the set, so this is sufficient.
OA is (B)
GMATT73 I see the point.
..this question has a very good trap.
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good question. I think it is B. I is just a condition but does not define refined numbers.
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what is the point?
I dont get it...(1) and (2) are saying the same thing...I would say such a twisted question will never appear on the GMAT!
believe2 wrote: GMATT73 wrote: 1. Statement 1 tells us that a refined number must be a multiple of 22. This is a necessary, but not sufficient condition for a refined number. While every refined number is a multiple of 22, every multiple of 22 is not necessarily a refined number. Since we have no other info about the definition of a refined number, we cannot determine how many integers from 1-1000 fit that definition. Insuff.
2. Statement 2 provides us with a definition of a refined number- an even multiple of 11. We can find the number of even multiples of 11 in the set, so this is sufficient.
OA is (B) GMATT73 I see the point. ..this question has a very good trap. |
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fresinha12 wrote: what is the point? I dont get it...(1) and (2) are saying the same thing...I would say such a twisted question will never appear on the GMAT! believe2 wrote: GMATT73 wrote: 1. Statement 1 tells us that a refined number must be a multiple of 22. This is a necessary, but not sufficient condition for a refined number. While every refined number is a multiple of 22, every multiple of 22 is not necessarily a refined number. Since we have no other info about the definition of a refined number, we cannot determine how many integers from 1-1000 fit that definition. Insuff.
2. Statement 2 provides us with a definition of a refined number- an even multiple of 11. We can find the number of even multiples of 11 in the set, so this is sufficient.
OA is (B) GMATT73 I see the point. ..this question has a very good trap. the diff b/w 1) and 2) is that in 1) 22 and 44 may be refined numbers. we can calc the prob. 22 44 66 may be refinded numbers as well. the prob to the former example is different but both satisfy 1). in 2) its certain that every mutiple off 22 is a refined number. there is only one value for the prob.
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fresinha12 wrote: what is the point?
I dont get it...(1) and (2) are saying the same thing...I would say such a twisted question will never appear on the GMAT!
Yes I've seen this question type in the GMAT test. The trap is (1) doesn't define "refined number" and (2) does.
For example, you can say "an even number must be an integer", this doesn't define an even number, because not every integer is an even number. Similarly with (1), every refined number must be divided by 22. But perhaps they also must be divided by 4, or something else.
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Re: If a number is drawn at random from the first 1000 positive [#permalink]
25 Dec 2012, 07:30
Sorry for starting this old thread, but can anyone please elaborate on this ancient problem? I am still not able to distinguish 1 and 2, apart from considering that one is definition and the other is not. Need examples for clarification.
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Re: If a number is drawn at random from the first 1000 positive [#permalink]
25 Dec 2012, 08:12
Marcab wrote: Sorry for starting this old thread, but can anyone please elaborate on this ancient problem? I am still not able to distinguish 1 and 2, apart from considering that one is definition and the other is not. Need examples for clarification. I would say it's more about the wording than the math. Let's make it simple. 1. Any refined number must be divisible by 22 If refined numbers were 44n then (1) would give us wrong numbers. 44, 88, 132 = refined. But (1) doesn't tell us that 22, 44, 110 is not refined. 2. A refined number is any even multiple of 11. Here we're told the actual definition of refined numbers. They're the even multiples of 11. 11*2 11*4 11*6 and so on. This doesn't leave any blind spots or confusion.
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Re: If a number is drawn at random from the first 1000 positive
[#permalink]
25 Dec 2012, 08:12
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