Answer
$0.4\%$
Work Step by Step
The margin of error of a sample size $n$ is a $95\%$ probability that a sample lies within the margin of error which is $\pm\frac{1}{\sqrt n}\cdot 100\%$ Hence here the margin of error: $\pm\frac{1}{\sqrt {10000}}\cdot 100\%=\pm1\%$.
Thus it improved the margin of error by $1.4\%-1\%=0.4\%$
