The first question: (1-2)+(3-4)+++(2001-2002) One * * is a group of 1001, so the answer is-100 1.

Second question: 99...9(2000 nines) × 99 ... 9 (2000 nines)+1 99...9 (2000 nines) can be regarded as 1000...0 (one * * two thousand zeros.