EMPOWERgmatRichC
QUANT 4-PACK SERIES Problem Solving Pack 4 Question 3 If a, b and c are consecutive...If a, b and c are consecutive positive integers and a < b < c, then what is the minimum possible value of
\(3^{2bc}\) / \(3^{2ab}\)
A) 81
B) 2,187
C) 3,300
D) 6,561
E) 19,683
Hi All,
To start, the answer choices to this question are rather 'spread out', so we might be able to use that spread to our advantage (and avoid some calculations).
We're told that a, b and c are consecutive positive integers and a < b < c. We're asked for the MINIMUM value of \(3^{2bc}\) / \(3^{2ab}\)...
Since the prompt asks for the MINIMUM value, it's likely that we'll have to make the 3 variables as small as possible, but we'll have to check to make sure that that's what is required to get to the correct answer. The smallest 3 numbers that 'fit' are...
a = 1
b = 2
c = 3
This makes the calculation...
\(3^{12}\) / \(3^{4}\) = \(3^{8}\)
\(3^{8}\)= \(9^{4}\) = \(81^{2}\) = ABOUT \(80^{2}\) = ABOUT 6400, so the answer appears to be D. We just need to confirm that that's the case....
IF....
a = 2
b = 3
c = 4
This makes the calculation...
\(3^{24}\) / \(3^{12}\) = \(3^{12}\)
\(3^{12}\) is clearly bigger than \(3^{8}\), meaning that increasing the values of a, b and c will lead to a LARGER end result. This proves that D is actually the smallest possible result.
Final Answer:
GMAT assassins aren't born, they're made,
Rich