绍兴市2006年初中数学学业考中有一道这样的试题:某校部分住校生,放学后到学校锅炉房打水,每人接水2升,他们先同时打开两个放水龙头,后来因故障关闭一个放水龙头.假设前后两人接水间隔时间忽略不计,且不发生泼洒,锅炉内的余水量 y(升)与接水时间 x(分)的函数图象如图1. Shaoxing City, 2006 junior high school mathematics test in a test such questions: a school part of the students, after school to the school boiler room water, each received 2 liters of water, they first simultaneously open two tap, and later closed due to failure A faucet.If the two before and after the water interval is neglected, and does not spill, the amount of water in the boiler y (l) and the water receiving time x (minutes) image of the function shown in Figure 1.