Let the weights of the five boxes, in increasing order be A, B, C, D and E. i.e. A < B < C < D < E. Each of the boxes can be paired up with another box in a total of 4 ways. If we sum up all the given weights, we get 4(A+ B+ C+ D+ E)= (110 + 112+113+114+115 + 116 + 117 + 118+120 + 121) = 1156 kg ⇒ A + B + C + D + E = 289 kg ...(i) Now, 121 kg is the sum of the weight of the boxes D and E and 110 is the sum of the weights of the boxes A and B. i.e. A+B = 110kg and D + E = 121 kg A + B + D + E= 231 kg ... (ii) Subtracting Eq. (ii) from Eq. (i), we get C =289-231 = 58 kg Now, 120 kg is the sum of the weights of the boxes C and E i.e C+E = 120kg ⇒ E = (120 - 58) kg = 62 kg