Đáp án đúng: C
Giải chi tiết:Ta có:
\(\begin{array}{l}S \times 3 = 1 \times 2 \times 3 + 2 \times 3 \times 3 + 3 \times 4 \times 3 + .... + 98 \times 99 \times 3\\\,\,\,\,\,\,\,\,\,\, = \,1 \times 2 \times \left( {3 - 0} \right) + 2 \times 3 \times \left( {4 - 1} \right) + 3 \times 4 \times \left( {5 - 2} \right) + .... + 98 \times 99 \times \left( {100 - 97} \right)\\\,\,\,\,\,\,\,\,\,\, = \,\left( {1 \times 2 \times 3 - 0 \times 1 \times 2} \right) + \left( {2 \times 3 \times 4 - 1 \times 2 \times 3} \right) + \left( {3 \times 4 \times 5 - 2 \times 3 \times 4} \right) + ... + \left( {98 \times 99 \times 100 - 97 \times 98 \times 99} \right)\\\,\,\,\,\,\,\,\,\,\, = \,98 \times 99 \times 100 - 0 \times 1 \times 2\\\,\,\,\,\,\,\,\,\,\, = 98 \times 99 \times 100\end{array}\)
Vậy \(S = 98 \times 99 \times 100:3 = 323\,400\).
Đáp số: 323400.
Chọn C
