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Primes/Exponents: If x, y, and z are integers greater than 1
Hmmm why did the discussion on this stop? Because according to the MGMAT, the OA is B!!!
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Stuart@KaplanGMAT
- GMAT Instructor
- Posts: 3225
- Location: Toronto
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Because the original post misstated statement (1) (in the OP, statement 1 tells us that z is prime; in the actual question, statement 1 tells us that y is prime), so the MGMAT explanation for statement 1 doesn't apply to this thread.abcdefg wrote:Hmmm why did the discussion on this stop? Because according to the MGMAT, the OA is B!!!
Stuart Kovinsky | Kaplan GMAT Faculty | Toronto
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For the original problem (where statement 1 states that y is prime rather than z is prime):
5^2 * z = 3 * x^y
Case 1) 5^2 * 3 = 3 * 5^2
Case 2) 5^2 * 3 = 3 * 25^1
Case 3) 5^2 * (3*5^2) = 3 * 25^2
If Y is prime (y>=2), then that rules out Case 2 but not Case 1 and Case 3. So (1) is insufficient.
If X is prime (x>=2), then that rules out Case 2 and Case 3, but not Case 1. So (2) is sufficient.
Answer is B.
5^2 * z = 3 * x^y
Case 1) 5^2 * 3 = 3 * 5^2
Case 2) 5^2 * 3 = 3 * 25^1
Case 3) 5^2 * (3*5^2) = 3 * 25^2
If Y is prime (y>=2), then that rules out Case 2 but not Case 1 and Case 3. So (1) is insufficient.
If X is prime (x>=2), then that rules out Case 2 and Case 3, but not Case 1. So (2) is sufficient.
Answer is B.
Last edited by gkumar on Sat Oct 17, 2009 9:14 pm, edited 1 time in total.
Yes, the problem was incorrectly stated. But it's interesting to see how Z plays a role too. Thanks for the explanation for the problem twist, Stuart.
But if we were to use the incorrectly stated problem
1) z is prime (instead of y is prime as per the original question)
2) x is prime
Then wouldn't the answer be B anyway???
5^2 * z = 3 * x^y
Case 1) 5^2 * 3 = 3 * 5^2
Case 2) 5^2 * 3 = 3 * 25^1
Case 3) 5^2 * (3*5^2) = 3 * 25^2
If Z is prime (z>=2), then that rules out Case 3 but not Case 2 and Case 3. So (1) is insufficient.
If X is prime (x>=2), then that rules out Case 2 and Case 3, but not Case 1. So (2) is sufficient.
Answer is B, and not D? Please clarify. Thanks!
But if we were to use the incorrectly stated problem
1) z is prime (instead of y is prime as per the original question)
2) x is prime
Then wouldn't the answer be B anyway???
5^2 * z = 3 * x^y
Case 1) 5^2 * 3 = 3 * 5^2
Case 2) 5^2 * 3 = 3 * 25^1
Case 3) 5^2 * (3*5^2) = 3 * 25^2
If Z is prime (z>=2), then that rules out Case 3 but not Case 2 and Case 3. So (1) is insufficient.
If X is prime (x>=2), then that rules out Case 2 and Case 3, but not Case 1. So (2) is sufficient.
Answer is B, and not D? Please clarify. Thanks!
-
Stuart@KaplanGMAT
- GMAT Instructor
- Posts: 3225
- Location: Toronto
- Thanked: 1710 times
- GMAT Score:800
Nope - the original question tells us that x, y and z are all greater than 1. In case 2 you have y=1, which is impossible; therefore, case 2 is also ruled out.gkumar wrote:Yes, the problem was incorrectly stated. But it's interesting to see how Z plays a role too. Thanks for the explanation for the problem twist, Stuart.
But if we were to use the incorrectly stated problem
1) z is prime (instead of y is prime as per the original question)
2) x is prime
Then wouldn't the answer be B anyway???
5^2 * z = 3 * x^y
Case 1) 5^2 * 3 = 3 * 5^2
Case 2) 5^2 * 3 = 3 * 25^1
Case 3) 5^2 * (3*5^2) = 3 * 25^2
If Z is prime (z>=2), then that rules out Case 3 but not Case 2 and Case 3. So (1) is insufficient.
If X is prime (x>=2), then that rules out Case 2 and Case 3, but not Case 1. So (2) is sufficient.
Answer is B, and not D? Please clarify. Thanks!
Stuart Kovinsky | Kaplan GMAT Faculty | Toronto
Kaplan Exclusive: The Official Test Day Experience | Ready to Take a Free Practice Test? | Kaplan/Beat the GMAT Member Discount
BTG100 for $100 off a full course
