Which of the following ordered pairs lies on the line $y = x$?

Which of the following ordered pairs lies on the line $y = x$?
  1. $(2,3)$
  2. $(-4,4)$
  3. $(5,5)$
  4. $(0,1)$

Solution

On the line $y=x$, both coordinates are equal. Only $(5,5)$ has $y=x$.

Asked in: IMO

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