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MathRevolution
[Math Revolution GMAT math practice question]

If \(x\) and \(y\) are prime numbers, how many factors has \(x^2y^2\)?

1) \(xy=10\)
2) \(x+y\) is odd


Note: x and y are prime numbers.

We are looking for the number of factors of \(x^2y^2\).

Total number of factors = (2+1) (2+1) = 3*3 = 9.

is this question okay ? or i am wrong.
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=>

Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.

The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question.

If \(x\) and \(y\) are different prime numbers, then \(xy\) has \((2+1)(2+1) = 9\) factors.
If \(x\) and \(y\) are the same prime number, then \(xy\) has \(4+1 = 5\) factors.

Condition 1)
Since \(x\) and \(y\) are prime numbers and \(xy = 10\), either \(x = 2\) and \(y = 5,\) or \(x = 5\) and \(y = 2.\)
So, \(x\) and \(y\) are different prime numbers. Thus, condition 1) is sufficient.

Condition 2)
Since \(x\) and \(y\) are prime numbers and \(x + y\) is odd, one of them is even and the other one is odd.
So, \(x\) and \(y\) are different prime numbers. Thus, condition 2) is sufficient.

Therefore, D is the answer.

Answer: D
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MathRevolution
[Math Revolution GMAT math practice question]

If \(x\) and \(y\) are prime numbers, how many factors has \(x^2y^2\)?

1) \(xy=10\)
2) \(x+y\) is odd


Note: x and y are prime numbers.

We are looking for the number of factors of \(x^2y^2\).

Total number of factors = (2+1) (2+1) = 3*3 = 9.

is this question okay ? or i am wrong.

That is right.
The point of this question is that x and y are different prime number or not.
From each of conditions, we can conclude x and y are different prime numbers, and the number of factors is (2+1)(2+1) = 3.
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MathRevolution
[Math Revolution GMAT math practice question]

If \(x\) and \(y\) are prime numbers, how many factors has \(x^2y^2\)?

1) \(xy=10\)
2) \(x+y\) is odd


Good Question!

x and y are primes - could be 2 and any other prime number or any other prime pair (apart from 2)

1. xy =10 ; possibility - 2 and 5 (sufficient)

2. x + y = odd -- here again the possiblilty is 2 and any other number ( sufficient)

D
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