Cho hình chóp S.ABCD. 

C

- Hướng dẫn giải

Đáp án C

Ta có $\frac{V_{S.A\text{'}B\text{'}C\text{'}}}{V_{S.ABC}}=\frac{SA\text{'}}{SA}.\frac{SB\text{'}}{SB}.\frac{SC\text{'}}{SC}=\frac{1}{8}$ và $\frac{V_{S.A\text{'}D\text{'}C\text{'}}}{V_{S.ADC}}=\frac{SA\text{'}}{SA}.\frac{SD\text{'}}{SD}.\frac{SC\text{'}}{SC}=\frac{1}{8}$ 

Mà $V_{S.ABC}=V_{S.ADC}=\frac{1}{2}{V}_{S.ABCD}\Rightarrow V_{S.A\text{'}B\text{'}C\text{'}}+V_{S.A\text{'}D\text{'}C\text{'}}=\frac{V_{S.ABCD}}{8}\iff \frac{V_{S.A\text{'}B\text{'}C\text{'}D\text{'}}}{V_{S.ABCD}}=\frac{1}{8}$.