Three runners $X$, $Y$ and $Z$ start together. After $10$ minutes, $X$ has covered $1$ km, $Y$ $1.5$ km and…

Three runners $X$, $Y$ and $Z$ start together. After $10$ minutes, $X$ has covered $1$ km, $Y$ $1.5$ km and $Z$ $2$ km. From their distance-time graphs, the order from fastest to slowest is:
  1. $X, Y, Z$
  2. $Z, Y, X$
  3. $Y, X, Z$
  4. $Y, Z, X$

Solution

More distance in the same time means faster. Distances: $Z(2)>Y(1.5)>X(1)$, so order is $Z,Y,X$.

Asked in: IMO

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