The cost of a notebook is twice the cost of a pen. Write a linear equation in two variables to represent this statement.

(Take the cost of a notebook to be Rs x and that of a pen to be Rs y.)
Solution:

Let the cost of a notebook and a pen be $x$ and $y$ respectively.

Cost of notebook $=2 \times$ Cost of pen

$x=2 y$

$x-2 y=0$
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