Which of the following CANNOT be weighed using a balance scale and these unit weights: 2, 4, 7, and 10\nOptions:\n(A) 16\n(B) 15\n(C) 18\n(D) 19\n(E) 21 Hmmm, my stream of consciousness:
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A. 13 (can be weighed by keeping weights of 10, 2 and 4 )\nB. 15 (cannot be weighed)\nC. 17 (can be weighed by keeping weights of 10 and 7 kg)\nD. 19(can be weighed by keeping weights of 10, 2 and 7 kg)\nE. 21 (can be weighed by keeping weights of 10, 7 and 4 kg) So, the answer is (B).
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