CAT (QA) PYQs

If a certain weight of an alloy of silver and copper is mixed with $3$ kg of pure silver, the resulting alloy will have $90\%$ silver by weight. If the same weight of the initial alloy is mixed with $2$ kg of another alloy which has $90\%$ silver by weight, the resulting alloy will have $84\%$ silver by weight. Then, the weight of the initial alloy, in kg, is

Consider three mixtures - the first having water and liquid A in the ratio $1: 2$, the second having water and liquid B in the ratio $1: 3$, and the third having water and liquid $C$ in the ratio $1: 4$. These three mixtures of $A, B,$ and $C$, respectively, are further mixed in the proportion $4:3:2$. Then the resulting mixture has

A $20 \%$ ethanol solution is mixed with another ethanol solution, say, $S$ of unknown concentration in the proportion $1:3$ by volume. This mixture is then mixed with an equal volume of $20 \%$ ethanol solution. If the resultant mixture is a $31.25 \%$ ethanol solution, then the unknown concentration of $S$ is