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Mathematics · 2025 · 1 mark
CBSE 2025 · Region 4 · Set 3 · Q7
If A and B are invertible matrices of order 3 × 3 such that det ( A )=4 and det [( AB )^-1]=1/20, then det ( B ) is equal to:
If A and B are invertible matrices of order $\displaystyle 3 \times 3$ such that $\displaystyle \operatorname{det}(\mathrm{A})=4$ and $\displaystyle \operatorname{det}\left[(\mathrm{AB})^{-1}\right]=\frac{1}{20}$, then $\displaystyle \operatorname{det}(\mathrm{B})$ is equal to :
Official answer
(D)
$\displaystyle 5$
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CBSE Class 12 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.