=> y*(1+2+3+4+.........+10)=49,5
=> y*(10+1).10:2=49,5
=> y*11.10:2=49,5
=> y*110:2=49,5
=> y*110=49,5*2
=> y=99:110
=> y=0,9
y+2 x y+3 x y+.....+10 x y=49,5
=>y x (1+2+3+....+10)=49,5
Tứ ->10 có:10-1+1=10(số hạng)
=>1+2+3+...+10=\(\frac{10x\left(10+1\right)}{2}=\frac{10x11}{2}=\frac{110}{2}=55\)
=>y x 55=49,5
=>y=49,5:55=>y=0,9
y+2*y+........+10*y=49,5
(1+2+........+10)*y=49,5
55*y=49,5
y=49,5:55
y=0,9