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For 'ones digit'- Need '1', '2', '3' and '4' to make weights from 1 to 9.
For 'tenth digit'- Need '10', '20', '30' and '40' to make weights from 11 to 99 + the weights from 'ones digit' combinations
For 'hundredth digit' - Need '100', '200' to make weights from 100 to 300 + weights from 'ones digit' and 'tenth digit' combinations.

So total: 10 weights. (D)
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1 gram, 2 gram, 4 gram, 8 gram, 16 gram, 32 gram, 64 gram, 128 gram, 256 gram i.e total 9 nos
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Bunuel
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A renowned medical store must purchase a set of n metal weights, each weighing an integer number of grams, such that all integer weights from 1 to 300 grams (inclusive) can be made with a combination of one or more of the weights. What is the minimum number of metal weights that the medical store must purchase?

(A) 6
(B) 8
(C) 9
(D) 10
(E) 12

We can begin the process by starting with the smallest weight, 1 gram. Using this weight alone, we can only weigh 1 gram, but not 2 grams. However, by adding the weight of 2 grams, we can weigh 1 gram, 2 grams, and 3 grams, but not 4 grams. Again, adding the weight of 4 grams, we can weigh 1 gram, 2 grams, 3 grams, 4 grams, 5 grams, 6 grams, and 7 grams, but not 8 grams.

To weigh the weight of the next power of 2, we always need to include the weight of that power of 2. For example, to weigh 8 grams, we need a weight of 8 grams. Continuing this process, we can observe that we can never weigh the weight of the next power of 2 without the weight of that power of 2.

For example:
1 gram, 2 grams, 4 grams, and 8 grams will allow us to weigh all weights up to 15 grams.
1 gram, 2 grams, 4 grams, 8 grams, and 16 grams will allow us to weigh all weights up to 31 grams.
...
1 gram, 2 grams, 4 grams, 8 grams, 16 grams, 32 grams, 64 grams, and 128 grams (8 weights), will allow us to weigh any weight up to 255 grams.
1 gram, 2 grams, 4 grams, 8 grams, 16 grams, 32 grams, 64 grams, 128 grams, and 256 grams (9 weights) will allow us to weigh any weight up to 511 grams.

Therefore, the minimum number of weights the store needs to purchase is 9.

Answer: C.

Also, consider this similar challenging question: https://gmatclub.com/forum/a-scientist- ... 02036.html


Why can't I weigh 8 with 1,2,3 and 4g. The question says one or more combinations. 4+3+1 = 8.

Posted from my mobile device
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adewale223
Bunuel
Bunuel
A renowned medical store must purchase a set of n metal weights, each weighing an integer number of grams, such that all integer weights from 1 to 300 grams (inclusive) can be made with a combination of one or more of the weights. What is the minimum number of metal weights that the medical store must purchase?

(A) 6
(B) 8
(C) 9
(D) 10
(E) 12

We can begin the process by starting with the smallest weight, 1 gram. Using this weight alone, we can only weigh 1 gram, but not 2 grams. However, by adding the weight of 2 grams, we can weigh 1 gram, 2 grams, and 3 grams, but not 4 grams. Again, adding the weight of 4 grams, we can weigh 1 gram, 2 grams, 3 grams, 4 grams, 5 grams, 6 grams, and 7 grams, but not 8 grams.

To weigh the weight of the next power of 2, we always need to include the weight of that power of 2. For example, to weigh 8 grams, we need a weight of 8 grams. Continuing this process, we can observe that we can never weigh the weight of the next power of 2 without the weight of that power of 2.

For example:
1 gram, 2 grams, 4 grams, and 8 grams will allow us to weigh all weights up to 15 grams.
1 gram, 2 grams, 4 grams, 8 grams, and 16 grams will allow us to weigh all weights up to 31 grams.
...
1 gram, 2 grams, 4 grams, 8 grams, 16 grams, 32 grams, 64 grams, and 128 grams (8 weights), will allow us to weigh any weight up to 255 grams.
1 gram, 2 grams, 4 grams, 8 grams, 16 grams, 32 grams, 64 grams, 128 grams, and 256 grams (9 weights) will allow us to weigh any weight up to 511 grams.

Therefore, the minimum number of weights the store needs to purchase is 9.

Answer: C.

Also, consider this similar challenging question: https://gmatclub.com/forum/a-scientist- ... 02036.html


Why can't I weigh 8 with 1,2,3 and 4g. The question says one or more combinations. 4+3+1 = 8.

Posted from my mobile device

We don't have 3gr weight. We have 1, 2, and 4 grams. With them we cannot weight 8 grams.
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Quote:

Quote:

Quote:
We don't have 3gr weight. We have 1, 2, and 4 grams. With them we cannot weight 8 grams.
­where does it say we don't have 3 gram weight?, is this common knowledge  :o and will such questions come as official questions?­
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Manifesting710

­where does it say we don't have 3 gram weight?, is this common knowledge  :o and will such questions come as official questions?­
­
The question is fine. We are minimizing the number of metal weights. Since we can weight 3 grams with 1 and 2-gram weights, we don't need a 3-gram weight itself.
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I used the approach as Bunuel explained but took me about 7 minutes to think through. I am sure there should be a faster way to approach this kind of problem which is more of logic. A good one though.
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