## Thinking Mathematically (6th Edition)

One variable is not sufficient when there is more than one variable is there. e.g. \begin{align} & x=10y+20z \\ & y=5x+10z \\ & z=x+y \\ \end{align} In this case we need to solve all three variables to get the solution. One variable is not sufficient to solve this equation. Hence, the provided statement does not make sense.