Số trung bình cộng là:

- Hướng dẫn giải

Số trung bình cộng là:

$\begin{array}{l}\overline{X}=\frac{4.6+5.4+6.3+7.2+8.8+9.5+10.4+11.3+12.1}{36}=\frac{270}{36}=7,5\\ \overline{X}=\frac{40.1+45.3+50.3+65.4+70.5+75.3+85.2+90.1+100.2+135.1+140.1+150.2}{60}\\ =\frac{2295}{30}=76,5(K\text{w/h)}\\ {\text{M}}_0=33\\ \overline{X}=\frac{30.30+31.60+32.95+33.110+34.120+35.85+36.40}{540}=\frac{17925}{540}\approx 33,19\\ \frac{30.5+35.8+40.9+45.8}{30}=\frac{1150}{30}\approx 38,3\\ \frac{40.9+45.7+50.6+55.n+60.8}{9+7+6+n+8}=52\\ \Rightarrow \frac{1455+55.n}{30+n}=52\\ \Rightarrow 1455+55.n=52.(30+n)\\ \Rightarrow 55.n-52.n=1560-1455\\ \Rightarrow 3.n=105\\ \Rightarrow n=35\backslash M_0=18\\ N=35\iff 3+y+5+7+9=35\iff 24+y=35\iff y=35-24=11\\ \frac{15.3+18.11+22.5+24.7+9x}{35}=19\\ \iff \frac{521+9x}{35}=19\\ \iff 521+9x=665\\ \iff 9x=144\\ \iff x=16\end{array}$

$\overline{X}=\frac{4.6+5.4+6.3+7.2+8.8+9.5+10.4+11.3+12.1}{36}=\frac{270}{36}=7,5$ (phút)

 Đáp án cần chọn là C