10/(1*2)+20/(1*2*3)+30/(1*2*3*4)+40/(1*2*3*4*5)++...+90/(1*2

10/(1*2)+20/(1*2*3)+30/(1*2*3*4)+40/(1*2*3*4*5)+...+90/(1*2* 10/(1*2)+20/(1*2*3)+30/(1*2*3*4)+40/(1*2*3*4*5)++...+90/(1*2 1*2*3+2*4*6+...10*20*30/2*3*4+...+20*30*40 1+2+3+4+10+20+30+40+1234=? 4.{1,5,10}{2,10,20}{3,15,30}{4,20,40}{ }. 1/1×2+1/2×3+1/3×4+1/4×5+...+1/39×40 1/2+1/3+2/3+1/4+2/4+3/4+1/5+2/5+3/5+4/5.+1/40+2/40+.+38/40+3 1＝10 2＝20 3＝30 4＝40 5＝50 1+2+3+4+5+6+7+8+9+10+20+30+40+50.+100 1/1*2*3+1/2*3*4+1/3*4*5+.+1/18*19*20 1/1*2*3 + 1/2*3*4 + 1/3*4*5 +.+1/20*21*22 (1/2+1/3+1/4+…1/39+1/40)+(2/3+2/4+2/5+…2/39+2/40)+(3/4+3/5+3