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Joined: 23 Mar 2014
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If a, b, x and y are prime numbers and a^x + b^y = 129, what is the va
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14 Sep 2014, 15:33
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74% (02:01) correct 26% (02:28) wrong based on 206 sessions
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If a, b, x and y are prime numbers and a^x + b^y = 129, what is the value of x+y? (A) 5 (B) 6 (C) 10 (D) 13 (E) 15 Can someone explain how to approach this question systematically? Ie. what are your first couple steps in handling this question and how do you break it down?
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Re: If a, b, x and y are prime numbers and a^x + b^y = 129, what is the va
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26 Sep 2014, 22:59
beef001 wrote: If a, b, x and y are prime numbers and a^x + b^y = 129, what is the value of x+y?
(A) 5 (B) 6 (C) 10 (D) 13 (E) 15
Can someone explain how to approach this question systematically? Ie. what are your first couple steps in handling this question and how do you break it down? a^x + b^y = 129 (odd) all primes except 2 are odd. but if a and b are odd primes then odd+odd = even so one of a or b has to be 2. 2^x + b^y = 129 2^2 + 5^3 = 129
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Re: If a, b, x and y are prime numbers and a^x + b^y = 129, what is the va
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14 Sep 2014, 17:10
Hi, It should not be difficult, since simple testing 2 pares of primes gives the result. a(x) + b(y) = 129 11(2) + 2(3) = 129 x+y = 5
I think, that such questions do not have system approach, as they generally test the skills of correct Picking of numbers...



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Re: If a, b, x and y are prime numbers and a^x + b^y = 129, what is the va
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15 Sep 2014, 01:56
In fact 5^3+2^2=129 too...thus yielding x+y=5.



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Re: If a, b, x and y are prime numbers and a^x + b^y = 129, what is the va
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26 Aug 2017, 11:47
thefibonacci wrote: beef001 wrote: If a, b, x and y are prime numbers and a^x + b^y = 129, what is the value of x+y?
(A) 5 (B) 6 (C) 10 (D) 13 (E) 15
Can someone explain how to approach this question systematically? Ie. what are your first couple steps in handling this question and how do you break it down? a^x + b^y = 129 (odd) all primes except 2 are odd. but if a and b are odd primes then odd+odd = even so one of a or b has to be 2. 2^x + b^y = 129 2^2 + 5^3 = 129 Will leave it here). All prime numbers that can fit: 2, 3, 5, 7, 11. It is more comfortable to check first the closest to result (129) numbers. First option fits: 11^2 + 2^3 = 129 I also think there is no systematic approach in such cases, but you can use different prompts to solve them. In this case yo can use that: 1. One on of them has to be even, because 129 is odd, and all prime numbers are odd except of 2. So we have to have odd + even > one of them is 2. 2. 11^2 is the closest to 129, so it is in our best interests to check it first. 2^3 fits. No one saidthat a, b, x, y have to be different.



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Joined: 15 Feb 2018
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Re: If a, b, x and y are prime numbers and a^x + b^y = 129, what is the va
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14 Jan 2019, 00:34
BunuelCan process of elimination remove some options? Is there a different method than guessing combinations of 2^x+b^y?



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Joined: 03 Jun 2018
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Re: If a, b, x and y are prime numbers and a^x + b^y = 129, what is the va
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24 Jan 2019, 10:31
Hi, Shouldn't the answer be C? Because it is not mentioned that a, b x and y are same prime nos. or that we hav to find the minimum value.
Can someone calrify?



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Re: If a, b, x and y are prime numbers and a^x + b^y = 129, what is the va
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03 Mar 2019, 11:16
I leave here another option...
The statement does not tell us that they all are different.
\(11^2 + 2^3 = 129\)
2 + 3 = 5
A




Re: If a, b, x and y are prime numbers and a^x + b^y = 129, what is the va
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03 Mar 2019, 11:16






