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Mathematics · 2025 · 5 marks
CBSE 2025 · Region 5 · Set 2 · Q34
State the converse of basic proportionality theorem. Also find BF/FC in the following figure, given that AB ∥ DC ∥ EF and AE/ED=2/3. Also, find the…
State the converse of basic proportionality theorem. Also find $\displaystyle \frac{\mathrm{BF}}{\mathrm{FC}}$ in the following figure, given that $\displaystyle \mathrm{AB}\|\mathrm{DC}\| \mathrm{EF}$ and $\displaystyle \frac{\mathrm{AE}}{\mathrm{ED}}=\frac{2}{3}$. Also, find the length of EF if $\displaystyle \mathrm{AB}=10 \mathrm{~cm}$ and $\displaystyle \mathrm{DC}=15 \mathrm{~cm}$.

Marking-scheme solution
Correct statement of converse of Basic Proportionality Theorem.
In \(\displaystyle \Delta \mathrm{ADC}, \mathrm{EG} \| \mathrm{DC}\)
\[\Rightarrow \frac{\mathrm{AE}}{\mathrm{ED}}=\frac{\mathrm{AG}}{\mathrm{GC}}=\frac{2}{3}
\]
In \(\displaystyle \Delta \mathrm{ABC}, \mathrm{GF} \| \mathrm{AB}\)
\[\Rightarrow \frac{\mathrm{AG}}{\mathrm{GC}}=\frac{\mathrm{BF}}{\mathrm{FC}}=\frac{2}{2}
\]
\(\displaystyle \Delta \mathrm{AEG} \sim \Delta \mathrm{ADC}\)
\[\begin{aligned}
& \Rightarrow \frac{\mathrm{AE}}{\mathrm{AD}}=\frac{\mathrm{AG}}{\mathrm{AC}}=\frac{\mathrm{EG}}{\mathrm{DC}} \\
& \Rightarrow \frac{2}{5}=\frac{\mathrm{EG}}{\mathrm{DC}} \\
& \Rightarrow \mathrm{EG}=\frac{2}{5} \times 15=6 \mathrm{~cm} \\
& \text { Similarly, } \Delta \mathrm{CFG} \sim \Delta \mathrm{CBA} \text { and } \frac{\mathrm{FC}}{\mathrm{BF}}=\frac{3}{2} \\
& \Rightarrow \frac{\mathrm{FC}}{\mathrm{BC}}=\frac{\mathrm{GF}}{\mathrm{AB}}=\frac{3}{5} \\
& \Rightarrow \mathrm{GF}=\frac{3}{5} \times 10=6 \mathrm{~cm} \\
& \mathrm{EF}=\mathrm{EG}+\mathrm{GF}=6+6=12 \mathrm{~cm}
\end{aligned}
\]
\[\begin{aligned}
& \Rightarrow \frac{\mathrm{FC}}{\mathrm{BC}}=\frac{\mathrm{GF}}{\mathrm{AB}}=\frac{3}{5} \\
& \Rightarrow \mathrm{GF}=\frac{3}{5} \times 10=6 \mathrm{~cm}
\end{aligned}
\]
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CBSE Class 10 Mathematics past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.