Max@Math Revolution wrote:[GMAT math practice question]

If m and n are integers greater than 1, is m^n>500?

1) n>8
2) n>4m

1) The minimum m^n could be is 2^9 which is 512. Therefore, m^n will always be greater than 500.
----> SUFFICIENT

2)
Minimum m = 2
minimum n = 9
This is same info we got from statement 1
-----> SUFFICIENT

Answer: D

Max@Math Revolution wrote:[GMAT math practice question]

If m and n are integers greater than 1, is m^n>500?

1) n>8
2) n>4m

We see that the least integer m can be is 2. When m = 2, we see that the least integer that satisfies 2^m > 500 is m = 9, since 2^9 = 512 > 500.

Statement One Alone:

n > 8

We know that m must be at least 2. If n > 8, then n^m is at least 2^9 = 512. The answer to the question is yes. Statement one alone is sufficient.

Statement Two Alone:

n > 4m

Since m must be at least 2, we see that n > 8. Thus, we know that n^m is at least 2^9 = 512. The answer to the question is yes. Statement two alone is sufficient.

Answer: D

=>

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.

Since we have 2 variables (m and n) and 0 equations, C is most likely to be the answer. So, we should consider conditions 1) & 2) together first. After comparing the number of variables and the number of equations, we can save time by considering conditions 1) & 2) together first.

Conditions 1) & 2)
As the question asks if m^n > 500, we need to find the minimum possible value of m^n.
Since m ≥ 2 and n ≥ 9, the minimum possible value of m^n is 2^9 = 512 > 500.
Both conditions together are sufficient.

Since this question is an inequality question (one of the key question areas), CMT (Common Mistake Type) 4(A) of the VA (Variable Approach) method tells us that we should also check answers A and B.

Condition 1)
Since m ≥ 2 and n ≥ 9, the minimum possible value of m^n is 2^9 = 512 > 500.
Condition 1) is sufficient.

Condition 2)
Since m ≥ 2 and n > 4m ≥ 4*2 = 8, it follows that n ≥ 9 and m^n ≥ 2^9 = 512 > 500.
Condition 2) is sufficient, too.

Therefore, D is the answer.

Answer: D

Note: Since condition 1) is the same as condition 2), D is most likely to be the answer by Tip 1).

Normally, in problems which require 2 equations, such as those in which the original conditions include 2 variables, or 3 variables and 1 equation, or 4 variables and 2 equations, each of conditions 1) and 2) provide an additional equation. In these problems, the two key possibilities are that C is the answer (with probability 70%), and E is the answer (with probability 25%). Thus, there is only a 5% chance that A, B or D is the answer. This occurs in common mistake types 3 and 4. Since C (both conditions together are sufficient) is the most likely answer, we save time by first checking whether conditions 1) and 2) are sufficient, when taken together. Obviously, there may be cases in which the answer is A, B, D or E, but if conditions 1) and 2) are NOT sufficient when taken together, the answer must be E.