You don't need to do any calculations, just match choices: (L=17/2 * W=11 * H=5/2) * 12 reams
(17*11*5)/4 * 12
( 17*11*5 ) * 3 = Volume necessary
If you notice, it's 4 prime numbers, the answer must have ONLY these numbers, i.e. since it says "exactly" the volume must be the same, and the prime factorization of any n>1 is unique.
A. \(8 \frac{1}{2}\) in by 11 in by 12 in --> 17/2 * 11 * 3*4 --> 17 * 11 * 3 --> missing 5
B. 17 in by 11 in by 15 in --> 17*11*(5*3) --> this is correct
C. 17 in by 22 in by 3 in --> 17*(11*2) * 3 --> extra 2, missing 5
D. 51 in by 66 in by 15 in --> (17*3)*(11*6)*(5*3) --> extra 3^2 and 2
E. 102 in by 132 in by 30 in --> (17*6)(11*12)*(5*6) --> extra 3^2 and 2^4
Snezanelle
I approached the problem in a different way: I thought that 2,5 in is the width of the ream of paper so we
multiply it by 12 to get the needed space to hold all paper. I do understand that there is no information that 2,5 in is the width but it's a common logic to assume that other numbers (8,5 in and 11 in) are too big to be the width of a realm. We get 30 in as the 3rd dimension and our number in E.
What's wrong with my reasoning?
SnezanelleIt actually doesn't matter what you take as length, width, height because we're only multiplying. So if you have a L=2, W=4, H=6 rectangular solid, the volume would be 48. If you are stacking L=1, W=1, H=1 boxes, you could stack the boxes in different ways (for example 2*4*6 or 2*2*12, both Vol = 48). The idea is that you can take different L,W,H as long as they equate to the same volume. It's the same in this problem, other possible correct choices could be ( 51*11*5 ) or (17*33*5 ). The issue with answer E) is that it also multiplies the other dimensions, so in fact the volume is 72 times too large.
Side note: It becomes trickier when the dimensions of the object being stacked don't conform to the ratio of box (this problem says "exactly" so it's not an issue). In that case you have left over space or go over the max of at least 1 dimension (there's min-max problems that test this, where knowing Vol is not enough, you need to have the specific dimensions to say how many objects you can place in the box).
P.S. If experts can confirm my analysis it would be appreciated.