Tính 1 + 2 – 3 – 4 + 5 + 6 – 7 – 8 + 9 +…+ 994 – 995 – 996 + 997 + 998 = ?
Giải thích
1 + 2 – 3 – 4 + 5 + 6 – 7 – 8 + 9 +…+ 994 – 995 – 996 + 997 + 998
= 1 + (2 – 3 – 4 + 5) + (6 – 7 – 8 + 9) + …+ ( 994 – 995 – 996 + 997) + 998
= 1 + 0 + 0 +0 + …+ 0 + 998
= 1+ 998
= 999