Q:

A simple problem on ratio.

If a solution A which has milk to water in the ratio $7:4$ is mixed with solution B which has the ratio of water to milk as $9:2$ such that the ratio becomes $1:1$,then in what ratio were they mixed?
My work:
in solution A: milk=$7x$,water=$4x$ 
in solution B: milk=$9x$,water= $2x$
Now I can't think how to use third part(mixing of both solution.)

A:

Don't use $x$ for both solution $A$ and solution $B$ - use a different variable, because they refer to different things.
If we take $x$ units of solution $A$, we get $(7/11)x$ units of milk and $(4/11)x$ units of water.
If we take $y$ units of solution $B$, we get $(9/11)y$ units of milk and $(2/11)y$ units of water.
Suppose that mixing $x$ units of $A$ and $y$ units of $B$ results in a combination of milk and water that is in a ratio of $1:1$. Use this information to relate $x$ and $y$.

