✔ 最佳答案
37+44+51+58+65.........+709+716+723+730
No. of terms = 99
Each terms take out 30, then there is 99*30 = 2970
7+7*2+7*3+7*4+7*5+...+7*96+7*97+7*98+7*99
= 7(1+2+3+...+96+97+98+99)
= 7[(1+99)99)/2
= 34650
Hence,
37+44+51+58+65.........+709+716+723+730
= 7+7*2+7*3+7*4+7*5+...+7*96+7*97+7*98+7*99 + 2970
= 34650 + 2970
= 37620
2010-09-30 07:05:55 補充：
37+44+51+58+65.........+709+716+723+730
項數= 99
每項抽出30 30, 共抽出了 99*30 = 100*30 - 30 = 2970
7+7*2+7*3+7*4+7*5+...+7*96+7*97+7*98+7*99
= 7(1+2+3+...+96+97+98+99)
= 7[(1+99)99)/2
= 34650
所以
37+44+51+58+65.........+709+716+723+730
= 7+7*2+7*3+7*4+7*5+...+7*96+7*97+7*98+7*99 + 2970
= 34650 + 2970
= 37620
參考: Hope the solution can help you^^”
