13 14 15 16 17 18 1
1/(12*13)+1/(13*14)+1/(14*15)+1/(15*16)+1/(16*17)+1/(17*18)+
13,14,15,16,17,18填空,
12+13+14+15+16+17+18+19=()×()
20-18+17-16+15-14+13-12+11-10
13+14+15+16+17+18+19=?(巧妙算法)
11 12 13 14 15 16 17 18
13,14,15,16,17,18,19题怎么写?
10 14 13 17 19 12 15 18 16
11 12 13 14 15 16 17 18 19 20
1 2 4 5 6 9 10 12 13 14 15 16 17 18 20 21
20+19-18+17+16+15-14-13+……+4+3-2-1
计算:20+19-18-17+16+15-14-13+…+4+3-2-1.