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Câu 10:

`overline(X)=(42,5*4+47,5*14+52,5*8+57,5*10+62,5*6+67,5*2)/44~~ 53,2`

`=>` Chọn `A`

Câu 11:

GTTB: `x_1=2,85; x_2=3,15; x_3=3,45; x_4=3,75; x_5=4,05`

`overline(X)=(3*2,85+6*3,15+5*3,45+4*3,75+2*4,05)/(20)=3,39`

`s^2=1/20* (3*2,85^2+6*3,15^2+5*3,45^2+4*3,75^2+2*4,05^2)-3,39^2 =0,1314`

`=>` Chọn `C`

Câu 12:

GTTB: `x_1=22,5; x_2=27,5; x_3=32,5; x_4=37,5; x_5=42,5`

`overline(X)=(6* 22,5+6*27,5+4*32,5+1*37,5+1*42,5)/18=85/3`

`s^2=1/18* (6*22,5^2+6*27,5^2+4*32,5^2+1*37,5^2+1*42,5^2)-(85/3)^2=31,25`

`=>` Chọn `D`