1.7 density, 400 gr weight liquid is mixed with 1.2 density $600 \mathrm{gr}$ solution. Measuring the density $D$ of the newly formed solution, we find that $D=1.4$. What is the contraction that occurs when mixing the two initial liquids?
If there were no contraction, then the density $\delta$ of the 1000 g mixture could be calculated from the equality of volumes:

$$
\frac{1000}{\delta}=\frac{400}{1.7}+\frac{600}{1.2}, \text { hence } \delta=1.36
$$

Due to the contraction, the density is greater. Therefore, the volume of the mixture is: $\frac{1000}{D}=\frac{1000}{1.4}$, and thus the contraction is:

$$
\Delta V=\frac{400}{1.7}+\frac{600}{1.2}-\frac{1000}{1.4}=735.3-714.3=21 \mathrm{~cm}^{3}
$$

Branyitskai Nagy Iván (Ág. ev. g. VIII. o. Bp.)