6 c.c. of a 20% solution of alcohol in water is mixed with 4 c.c. of a 60% solution of alcohol in water. The alcoholic strength of the mixture is?

Answer: Option C

Quantity of alcohol in 10 c.c. solution
= (20% of 6 + 60% of 4) c.c.
= $$\left(\frac{20}{100}\times 6+\frac{60}{100}\times 4\right)$$    c.c.
= (1.2 + 2.4) c.c.
= 3.6 c.c.
∴ Required strength :
$$\begin{array}{rl}& =\left(\frac{3.6}{10}\times 100\right)\%\\ & =36\%\end{array}$$