Use some thinking to answer the following question. Which of the following CANNOT be weighed using a balance scale and these unit weights: 2, 4, 7, and 10
Options:
(A) 16
(B) 15
(C) 18
(D) 19
(E) 21
A. 13 (can be weighed by keeping weights of 10, 2 and 4 )
B. 15 (cannot be weighed)
C. 17 (can be weighed by keeping weights of 10 and 7 kg)
D. 19(can be weighed by keeping weights of 10, 2 and 7 kg)
E. 21 (can be weighed by keeping weights of 10, 7 and 4 kg) So the final answer is (B).