Question 39

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Jambmaths question: 

The binary operation defined on the set of real number is such that $x\oplus y=\frac{xy}{6}$for all $x,y\in \mathbb{R}$. Find the inverse of 20 under the operation when the identity element is 6

Option A: 

$\tfrac{1}{12}$

Option B: 

$\tfrac{10}{3}$

Option C: 

$\tfrac{1}{20}$

Option D: 

$\tfrac{9}{5}$

Jamb Maths Solution: 

$\begin{align}  & x\oplus y=\frac{xy}{6} \\ & 20\oplus {{20}^{-1}}=e \\ & \frac{20\times {{20}^{-1}}}{6}=6 \\ & 20\times {{20}^{-1}}=36 \\ & {{20}^{-1}}=\frac{36}{20}=\frac{9}{5} \\ & \text{The inverse of 20 (i}\text{.e}\text{.2}{{\text{0}}^{-1}})\text{ is }\frac{9}{5} \\\end{align}$

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