50 nha bạn

1. Sam said to his wife that he would phone her as soon as his plane landed in Boston.

2. Denis wanted to know how many Spanish lessons Linda had had previous week.

3. My father advised me not to wait till the next day.

4. He said that he wouldn't see me the following day.

5. He asked her where she was going.

6. I told her brought it back if it didn't fit.

7. She said to us not to try to open it then.

8. I asked her if it was going to be a fine day that day.

Theo đầu bài ta có:
\(S=1\cdot6+2\cdot9+3\cdot12+4\cdot15+...+98\cdot297+99\cdot300\)
\(=1\cdot\left(2\cdot3\right)+2\cdot\left(3\cdot3\right)+...+98\cdot\left(99\cdot3\right)+99\cdot\left(100\cdot3\right)\)
\(=1\cdot2\cdot3+2\cdot3\cdot\left(4-1\right)+...+98\cdot99\cdot\left(100-97\right)+99\cdot100\cdot\left(101-98\right)\)
\(=1\cdot2\cdot3+2\cdot3\cdot4-1\cdot2\cdot3+...+98\cdot99\cdot100-97\cdot98\cdot99+99\cdot100\cdot101-98\cdot99\cdot100\)
\(=99\cdot100\cdot101\)
\(=999900\)