The question is a little ambiguous or maybe I am confused. Can the number have only consecutive primes and no other number, If not I do not seem to be getting the answer
I go with A as its the only denominator which is a multiple of 900 which is the number of fav cases(all 3 digit numbers)
tough PS
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Source: Beat The GMAT — Problem Solving |
2 consecutive prime can be 2,3 or 3,5 or 5,7
number of numbers formed with 2,3 = 2^3 however, question is using exactly two consecutive primes so we have to remove the case 222 and 333 hence number of such numbers = 2^3-2 = 6
so, number of such numbers for 2,3..2,5 and 5,7 = 3*6 = 18
number of three digit number = 900
hence, answer is 18/900 = 1/50
none of the answer choice..
but i guess my method is correct !
number of numbers formed with 2,3 = 2^3 however, question is using exactly two consecutive primes so we have to remove the case 222 and 333 hence number of such numbers = 2^3-2 = 6
so, number of such numbers for 2,3..2,5 and 5,7 = 3*6 = 18
number of three digit number = 900
hence, answer is 18/900 = 1/50
none of the answer choice..
but i guess my method is correct !
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Stuart@KaplanGMAT
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Assuming this is the correct interpretation of the question:pops wrote:2 consecutive prime can be 2,3 or 3,5 or 5,7
number of numbers formed with 2,3 = 2^3 however, question is using exactly two consecutive primes so we have to remove the case 222 and 333 hence number of such numbers = 2^3-2 = 6
so, number of such numbers for 2,3..2,5 and 5,7 = 3*6 = 18
number of three digit number = 900
hence, answer is 18/900 = 1/50
none of the answer choice..
but i guess my method is correct !
correct.. we can us 2,3 or 3,5 or 5,7.
we need to use at least one from each pair, so our possible 3 digits are:
2,2,3
2,3,3
3,3,5
3,5,5
5,5,7
5,7,7
For each set, there are 3 different ways to arrange the number (e.g. 2,2,3 can be 223, 232 or 322),
So, we have 6*3 = 18 possible arrangements
and your calculation of 18/900 = 1/50 seems dead on.
So, we have to conclude that there's another "correct" interpretation of the question, solidifying my original thought that it's a very poorly worded question ("What's the probability of creating a 3 digit number?" Well, if I'm eating breakfast, the probability is very small!). Good news - you'd never see anything ambiguous on the actual GMAT.
What's the source of the question? In the future, please ALWAYS post the source, so we know whether we should take the question seriously or can just write it off.
Stuart Kovinsky | Kaplan GMAT Faculty | Toronto
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neoreaves
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I had noted this question a while back from another forum so I am not sure what the actual source is(Apologies) ...and I agree the question does seem ambigious ...I wanted to post this to be sure whether it was just me blaming the question or the questions was REALLY ambigious .....Anyways, ambiguity aside ...if the question was clearer I think it is a good question specially with Stuart's Explanation
