解：?$ \overline {x_{甲}}=(69+81+78+···+75)÷10=75.9(\mathrm {m})$?
?$ s^2_{甲}=\frac 1{10}×[(69-75.9)^2+(81-75.9)^2+···+(75-75.9)^2]=10.89(\mathrm {m^2})$?
?$ \overline {x_{乙}}=(74+76+76+···+67)÷10=74.9(\mathrm {m})$?
?$ s^2_{乙}=\frac 1{10}×[(74-74.9)^2+(76-74.9)^2+···+(67-74.9)^2]=20.69(\mathrm {m^2})$?
∵?$ s^2_{乙}>s^2_{甲}$?
∴甲型號的越野車剎車系統(tǒng)性能比較穩(wěn)定
