JEE Main 2020 · MathsMultiple choiceSingle correctMediumCalculation

JEE Main 9 January 2020, Shift 1, Maths Q54

Question 54 of 75 in this shift, Maths question 4 of 25, Section A.

If the matrices

\mathrm{A}=\begin{bmatrix}1&1&2\\1&3&4\\1&-1&3\end{bmatrix}

\mathrm{B}=\mathrm{adj}\,\mathrm{A}

and

\mathrm{C}=3\mathrm{A}

, then

\frac{|\mathrm{adj}\,\mathrm{B}|}{|\mathrm{C}|}

is equal to :

(1)2
(2)8Official answer
(3)16
(4)72

Official answer

Option 2

NTA final key (Jan 2020).

Chapter: Determinants
Topic: Matrix Inverse
Idea tested: Inverse Relation to Double Adjoint

Same idea in other shifts

Asked 16× in all

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6 Apr 2026, Shift 1 · Q21Let $A=\begin{bmatrix}-1&1&-1\\1&0&1\\0&0&1\end{bmatrix}$ satisfy…MediumNumerical value
7 Apr 2025, Shift 1 · Q5Let $A$ be a $3 \times 3$ matrix such that $|\mathrm{adj}(\mathrm{adj}(\mathrm{adj}\,A))| = 81$ . If…HardSingle correct
8 Apr 2025, Shift 2 · Q4Let $A = \begin{bmatrix} 2 & 2+p & 2+p+q \\ 4 & 6+2p & 8+3p+2q \\ 6 & 12+3p & 20+6p+3q \end{bmatrix}$ . If…MediumSingle correct
6 Apr 2024, Shift 2 · Q4If $A$ is a square matrix of order 3 such that $\det(A)=3$ and…MediumSingle correct
9 Apr 2024, Shift 1 · Q23Let A be a non-singular matrix of order 3. If $\det(3\,\mathrm{adj}(2\,\mathrm{adj}((\det A)A)))=3^{-13}\cdot2^{-10}$ and…HardNumerical value
30 Jan 2024, Shift 2 · Q3Let $R = \begin{pmatrix} x & 0 & 0 \\ 0 & y & 0 \\ 0 & 0 & z \end{pmatrix}$ be a non-zero $3\times 3$ matrix, where…HardOther
31 Jan 2024, Shift 2 · Q22Let A be a $3\times3$ matrix and $\det(A)=2$ . If…MediumNumerical value

Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.