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The "prime sum" of an integer n greater than 1 is the sum of [#permalink]
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05 Feb 2014, 02:26
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The Official Guide For GMAT® Quantitative Review, 2ND EditionThe "prime sum" of an integer n greater than 1 is the sum of all the prime factors of n, including repetitions. For example , the prime sum of 12 is 7, since 12 = 2 x 2 x 3 and 2 +2 + 3 = 7. For which of the following integers is the prime sum greater than 35 ? (A) 440 (b) 512 (C) 620 (D) 700 (E) 750 Problem Solving Question: 78 Category: Arithmetic Properties of numbers Page: 71 Difficulty: 600 GMAT Club is introducing a new project: The Official Guide For GMAT® Quantitative Review, 2ND Edition  Quantitative Questions ProjectEach week we'll be posting several questions from The Official Guide For GMAT® Quantitative Review, 2ND Edition and then after couple of days we'll provide Official Answer (OA) to them along with a slution. We'll be glad if you participate in development of this project: 1. Please provide your solutions to the questions; 2. Please vote for the best solutions by pressing Kudos button; 3. Please vote for the questions themselves by pressing Kudos button; 4. Please share your views on difficulty level of the questions, so that we have most precise evaluation. Thank you!
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Re: The "prime sum" of an integer n greater than 1 is the sum of [#permalink]
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05 Feb 2014, 02:27
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Re: The "prime sum" of an integer n greater than 1 is the sum of [#permalink]
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05 Feb 2014, 08:43
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Ans C
Solved it the prime factorization way 440= 2*2*2*5*11 Sum=22 512= 2^6 Sum=2*6=12 620=2*2*5*31 Sum=40>35 Hence correct.



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Re: The "prime sum" of an integer n greater than 1 is the sum of [#permalink]
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07 Feb 2014, 13:28
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I'd say (C) too, solved by the same method (took 1:14), might be timeconsuming if the answer was D, or E for example. I hope that a faster approach exists.



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Re: The "prime sum" of an integer n greater than 1 is the sum of [#permalink]
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07 Feb 2014, 14:59
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The "prime sum" of an integer n greater than 1 is the sum of all the prime factors of n, including repetitions. For example , the prime sum of 12 is 7, since 12 = 2 x 2 x 3 and 2 +2 + 3 = 7. For which of the following integers is the prime sum greater than 35 ? (A) 440 (b) 512 (C) 620 (D) 700 (E) 750 Before getting down to solving on careful observation B(2^9, So sum is 18),D(7*100> 7*2^2*5^2) and E(250*3>5^3*2*3) can be ruled out C looked good cause 620 is multiple of 31 so ideally should be the closest one.Always start with C and then decide to move on. Ans is C
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Re: The "prime sum" of an integer n greater than 1 is the sum of [#permalink]
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08 Feb 2014, 03:58



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Re: The "prime sum" of an integer n greater than 1 is the sum of [#permalink]
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09 Apr 2015, 07:32
Bunuel wrote: The Official Guide For GMAT® Quantitative Review, 2ND EditionThe "prime sum" of an integer n greater than 1 is the sum of all the prime factors of n, including repetitions. For example , the prime sum of 12 is 7, since 12 = 2 x 2 x 3 and 2 +2 + 3 = 7. For which of the following integers is the prime sum greater than 35 ? (A) 440 (b) 512 (C) 620 (D) 700 (E) 750 Problem Solving Question: 78 Category: Arithmetic Properties of numbers Page: 71 Difficulty: 600 GMAT Club is introducing a new project: The Official Guide For GMAT® Quantitative Review, 2ND Edition  Quantitative Questions ProjectEach week we'll be posting several questions from The Official Guide For GMAT® Quantitative Review, 2ND Edition and then after couple of days we'll provide Official Answer (OA) to them along with a slution. We'll be glad if you participate in development of this project: 1. Please provide your solutions to the questions; 2. Please vote for the best solutions by pressing Kudos button; 3. Please vote for the questions themselves by pressing Kudos button; 4. Please share your views on difficulty level of the questions, so that we have most precise evaluation. Thank you! we can see all options are even so 2 is common in all of them . only option B looks promising as 2*310 , 31 itself is very close to 35 . answer should be C.
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Re: The "prime sum" of an integer n greater than 1 is the sum of [#permalink]
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19 Apr 2015, 04:45
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Bunuel, you wrote that we shoud start by middle option. Can you explain the reason? Thanks.
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The "prime sum" of an integer n greater than 1 is the sum of [#permalink]
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Re: The "prime sum" of an integer n greater than 1 is the sum of [#permalink]
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19 Apr 2015, 06:15
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Thanks a lot. Makes sense now.
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Re: The "prime sum" of an integer n greater than 1 is the sum of [#permalink]
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18 May 2015, 03:27
Bunuel wrote: Ergenekon wrote: Bunuel, you wrote that we shoud start by middle option. Can you explain the reason? Thanks. Good question. +1. On the GMAT, answer choices are always in ascending/descending order, so trying option C firsts gives an idea which direction to go next if C is not correct. I always thought it would be good to start with B and then with D with ascending / descending order choices? That is exactly what I did and what took forever, because both B and D did not work...



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Re: The "prime sum" of an integer n greater than 1 is the sum of [#permalink]
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27 Mar 2016, 12:47
Bunuel wrote: Ergenekon wrote: Bunuel, you wrote that we shoud start by middle option. Can you explain the reason? Thanks. Good question. +1. On the GMAT, answer choices are always in ascending/descending order, so trying option C firsts gives an idea which direction to go next if C is not correct. Hello, except that we should have a way to assess in which direction to go, had C not worked... In such case, we should go toward the direction of the number having the bigger prime, or a repetition of prime high enough to increase "prime sum", which seems fairly difficult to assess (at least to me...) So should we not, because the question stem is structured with a " Which of the following", start with E upwards ? The assumption is that GMAT could be nasty enough to make us test more than 3 options... Indeed, we would stop at the first answer choice that works.



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Re: The "prime sum" of an integer n greater than 1 is the sum of [#permalink]
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12 Mar 2018, 07:05
Bunuel wrote: SOLUTION
The "prime sum" of an integer n greater than 1 is the sum of all the prime factors of n, including repetitions. For example , the prime sum of 12 is 7, since 12 = 2 x 2 x 3 and 2 +2 + 3 = 7. For which of the following integers is the prime sum greater than 35 ?
(A) 440 (B) 512 (C) 620 (D) 700 (E) 750
Start by testing the middle option:
(C) 620 = 2*2*5*31, hence the "prime sum" of 620 is 2 + 2 + 5 + 31 = 40 > 35. Since there can be only one correct answer, then it must be C.
Answer: C. Bunuel any idea how can I approximately eliminate other answer choices before I start doing prime factorization ? to save time I mean




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