Dr.Stat

Betrouwbaarheidsinterval:
$\overline{X}-\overline{Y}\pm z\times {\sigma }_{\overline{X}-\overline{Y}}$

${\sigma }_{\overline{X}-\overline{Y}}=\sqrt{\frac{{\sigma }_X^2}{n}+\frac{{\sigma }_Y^2}{m}}$

$\overline{X}=73$, $n=18$.
$\overline{Y}=65$, $m=25$.
${\sigma }_X=12$.
${\sigma }_Y=5$.

$\overline{X}-\overline{Y}=8$.
$z=2.57$.
${\sigma }_{\overline{X}-\overline{Y}}=3$.
$z\times {\sigma }_{\overline{X}-\overline{Y}}=7.71$