\(mean(x) = \frac{20t}{5} = 4t\\standard\hspace{1mm}deviation=\sqrt{\frac{10t^2}{5}}\\\sqrt{2}=\sqrt{\frac{10t^2}{5}}\\\sqrt{2}=\sqrt{2t^2}\\2 = 2t^2\\t^2=1\\t=1\)