=2x(1+2+...+16)
=2x(16+1)x16:2
=17x16
=272
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Các câu hỏi tương tự
tính nhanh : 10 + 11 + 12 + 13 + 14 + 15 + 16 + 1 7 + 18 + 19 + 20
3. Tính nhanh:
a, (1+3+5+7+9) - (0+2+4+6+8)=.........................................................................................
b, (11+13+15+17+19) - (10+12+14+16+18)=......................................................
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20=?
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20+...100=
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+.....+99999999999956214 (tính tỏng)
1+2-3-4+5+6-7-8+9+10-11-12+13+14-15-16+17+18-19-20...+301+302
Tính nhanh:
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19
11-12+13-14+15-16+17-18+19-20+21+22
(15x1-15)x(10+1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20)
Quá dễ phải hôn ^_^