1. Fill an empty live water truck with water, using three water pipes $A$, $B$, and $C$. If pipes $A$ and $C$ are used simultaneously, the truck is full when pipe $A$ has injected 4 tons of water; if pipes $B$ and $C$ are used simultaneously, the truck is full when pipe $B$ has injected 6 tons of water. It is known that the water injection rate of pipe $B$ is twice that of pipe $A$ per minute. How much water can the truck hold at most?
1. 【Answer】Solution: Let the water tanker can add $x$ tons of water
$$
\begin{array}{l}
\text { Then: Work efficiency ratio: } A: C=4:(x-4) ; B: C=6:(x-6) \\
\because A: B=1: 2 \\
\therefore \text { Let } A=12, B=24 \\
A: C=12:(3 x-12) \\
B: C=24:(4 x-24) \\
\therefore 3 x-12=4 x-24 \\
x=12
\end{array}
$$

Answer: The maximum amount of water that can be added is 12 tons.