KindRope
if m and n are positive integers such that m^3 is a factor of 3240 and n^4 is a multiple of 108, what is the minimum possible value of the product m.n ?
(A) 6
(B) 12
(C) 18
(D) 36
(E) 72
Step 1: Prime Factorization
3240 = 2^3 x 3^4 x 5^1
108 = 2^2 x 3^3
Step 2: Analyzing m^3 (factor of 3240)[ltr]

[/ltr]
[ltr]Since m3m cubed, its prime powers cannot exceed the powers in 3240. Also, since m3 is a perfect cube, its powers must be multiples of 3 (i.e., 0, 3, 6...).
[*]Max possible power of 2 in m3 ≤ 3 --> 2^3
Max possible power of 3 in m3 ≤ 4 --> 3^3
Max possible power of 5 in m3 ≤ 1 --> 5^0 = 1
So, the maximum possible value for m3 = 23 x 33 = 63 --> m ≤ 6
(Since we want to minimize m.n., we should check what values m can take. m can be 1, 2, 3, or 6).
[*]
Step 3: Analyzing n^4 (multiple of 108) [*]
Since n^4 is a multiple of 108, its prime powers must be greater than or equal to the powers in
108(2^2 x 3^3) Since n^4 is a perfect 4th power, its powers must be multiples of 4 (i.e., 0, 4, 8...).
Min power of 2 in n^4

≥ 2 --> 2^4
[ltr]

Min power of 3 in n^4

≥ 3 --> 3^4
So, the minimum possible value for n^4 = 2^4 x 3^4 = 6^4 --> Min n = 6[/ltr]
[/ltr]
[*]
Step 4: Minimizing the Product m.nWe know the minimum possible value of n is fixed at 6
to minimize m.n, we need the smallest positive integer value for m.
Since m is a positive integer, its absolute minimum value is 1 (and 1^3 = 1, which is a factor of 3240)
therefore Min(m.n) = 1 x 6 = 6
Answer (A)
Attachment:
GMAT-Club-Forum-2fwdjz0r.gif [ 43 Bytes | Viewed 32 times ]
Attachment:
GMAT-Club-Forum-id2wcb36.gif [ 43 Bytes | Viewed 33 times ]
Attachment:
GMAT-Club-Forum-wiba3uj1.gif [ 43 Bytes | Viewed 33 times ]
Attachment:
GMAT-Club-Forum-xlhr5zq7.gif [ 43 Bytes | Viewed 33 times ]
Attachment:
GMAT-Club-Forum-769afr96.gif [ 43 Bytes | Viewed 33 times ]