GRE Quant: Block Weighing Question

GRE Quant Problem Solving
1

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From this question, I get that it’s efficient to divide the blocks into groups of 3.

But my question is: If we divide 16 blocks into 5-5-6 and find out one of the 5 block group has the lighter block, we’ll divide the group into 2-2-1. If we weigh 2-2 and find out 2=2, then the 1 block group is the lighter block. Then, didn’t we find the lighter block in total of 2 weighings? Shouldn’t this mean that A=2 < B=3?

Thanks for any help in advance!

2

Does that have to be the case?

3

No, but I reckon it’s a possibility.

4

That’s not enough - notice the word “undoubtedly”. You don’t know at first that the block is in group 1/2 (i.e, the one with five blocks each).

5

I see. Thank you!