A U-tube is partially filled with water. Oil which does not mix with water is next poured into one side until water rises by 25 cm on the other side. If the density of oil is 0.8, the oil level will stand higher than the water level by

${\rho }_{\text{oil }}=0.8{\rho }_{\text{water }}=1$

When water goes down by x amount in one side of U-tube, then it moves up by x amount in other tube.
Thus, the total difference in height of water in both side is equal to 2x.

The difference in height of water: $h\text{'}=2\left(25\right)=50\mathrm{cm}$

${\mathrm{P}}_{\mathrm{A}}={\mathrm{P}}_{\mathrm{B}}$

$\Rightarrow {\mathrm{P}}_{\mathrm{o}}+{\rho }_{oil}\mathrm{gh}={\mathrm{P}}_{\mathrm{o}}+{\rho }_{\text{water }}\mathrm{g}\left(50\right)$

$\Rightarrow \left(0.8\right)gh=\left(1\right)g\left(50\right)$

$⟹\mathrm{h}=62.5\mathrm{cm}$

the oil stands higher than water by amount: $\mathrm{\Delta h}=\mathrm{h}-50=62.5-50=12.5 cm$