The average of 13 numbers is 58. Average of the first 7 of them is 57 and that of the last 7 is 61. Find the 8th number?\nOptions:\n(A) 72\n(B) 83\n(C) 45\n(D) 53\n(E) 64 Now, let's think a bit. Some random thoughts:
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Sum of all the 13 numbers = 13 * 58 = 754\nSum of the first 7 of them = 7 * 57 = 399\nSum of the last 7 of them = 7 * 61 = 427\nSo, the 8th number = 427 + 399 - 754 = 72.
The final answer: (A).
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