1992 AHSME Problems/Problem 21
Problem
For a finite sequence of numbers, the Cesáro sum of A is defined to be , where and . If the Cesáro sum of the 99-term sequence is 1000, what is the Cesáro sum of the 100-term sequence ?
Solution
Let us define the Cesáro total of a particular sequence to be n * Cesáro sum. We can see that the Cesáro total is \begin{align*} S_1 + S_2 + S_3 + ... + S_n \\ &= a_1 + (a_1 + a_2) + (a_1 + a_2 + a_3) + \ldots + (a_1 + a_2 + \ldots + a_n) \\ &= n \cdot a_1 + (n - 1) \cdot a_2 + \ldots + a_n. \end{align*} If we take this to be the Cesáro total for the second sequence, we can see that all the terms but the first term make up the first sequence. Since we know that the Cesáro total of the original sequence is than the Cesáro total of the second sequence is Thus the Cesáro sum of the second sequence is
See also
1992 AHSME (Problems • Answer Key • Resources) | ||
Preceded by Problem 20 |
Followed by Problem 22 | |
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