Question : In $\Delta \mathrm{ABC}$, a line parallel to side $\mathrm{BC}$ cuts the sides $\mathrm{AB}$ and $\mathrm{AC}$ at points $\mathrm{D}$ and $\mathrm{E}$ respectively and also point $\mathrm{D}$ divides $\mathrm{AB}$ in the ratio of $\mathrm{1 : 4}$. If the area of $\Delta \mathrm{ABC}$ is $200\;\mathrm{cm^2}$, then what is the area (in $\mathrm{cm^2}$) of quadrilateral $\mathrm{DECB}$?
Option 1: 192
Option 2: 50
Option 3: 120
Option 4: 96
Correct Answer: 192
Solution : Given: $\mathrm{AD:DB=1:4}$ and the area of $\Delta \mathrm{ABC}$ is $200\;\mathrm{cm^2}$. In $\Delta \mathrm{ABC}$, $\mathrm{DE}\parallel\mathrm{BC}$ So, $\Delta \mathrm{ADE}\sim\Delta \mathrm{ABC}$, The ratio of the areas of two similar triangles is equal to the square of the ratio of their corresponding sides. ⇒ $\frac{\text{Area of $\Delta \mathrm{ADE}$}}{{\text{Area of $\Delta \mathrm{ABC}$}}}=(\frac{\mathrm{AD}}{\mathrm{AB}})^2$ ⇒ $\frac{\text{Area of $\Delta \mathrm{ADE}$}}{{200}}=(\frac{\mathrm{1}}{\mathrm{5}})^2$ ⇒ $\frac{\text{Area of $\Delta \mathrm{ADE}$}}{{200}}=(\frac{\mathrm{1}}{\mathrm{25}})$ ⇒ $\text{Area of $\Delta \mathrm{ADE}$}=8\;\mathrm{cm^2}$ The area of quadrilateral $\mathrm{DECB}=\text{Area of $\Delta \mathrm{ABC}$}-\text{Area of $\Delta \mathrm{ADE}$}$ $=200\;\mathrm{cm^2}-8\;\mathrm{cm^2}=192\;\mathrm{cm^2}$ Hence, the correct answer is $192$.
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