为鼓励居民节约用水，某市自来水公司对全市用户采用分段计费的方式计算水费，收费标准如下
\u4e3a\u9f13\u52b1\u5c45\u6c11\u8282\u7ea6\u7528\u6c34\uff0c\u67d0\u5e02\u81ea\u6765\u6c34\u516c\u53f8\u5bf9\u5168\u5e02\u7528\u6237\u91c7\u7528\u5206\u6bb5\u8ba1\u8d39\u7684\u65b9\u5f0f\u8ba1\u7b97\u6c34\u8d39\uff0c\u6536\u8d39\u6807\u51c6\u5982\u4e0b1.
16\u5428\u6c34\u8d85\u8fc7\u4e8610\u5428\uff0c\u4e0d\u523018\u5428\uff0c\u654510\u5428\u4ee5\u5185\u7684\u6c34\u6bcf\u54282.2\u5143\uff0c\u517122\u5143
\u8d85\u8fc710\u5428\u7684\u6c34\u6bcf\u54282.8\u5143\uff0c\u51712.8\u00d76=16.8\u5143
\u603b\u5171\u4e3a
22+16.8=28.8\u5143
2.
\u5f53\u752818\u5428\u6c34\u65f6\uff0c\u8981\u4ea4\u8d39
22+2.8\u00d78=44.4\u5143
\u5219\u4e3a\u8d85\u8fc718\u5428\u90e8\u5206\u7684\u6c34\u4ed8\u6b3e\u4e3a
57.2-44.4=12.8\u5143
\u8fd9\u90e8\u5206\u6c34\u4f4d
12.8/3.2=4\u5428
\u6545\u7528\u6c34\u4e3a22\u5428
3.7\u6708\u4efd\u591a\u4ea4\u8d3912\u5143\uff0c\u7531\u4e8e\u8d85\u8fc718\u5428\uff0c\u52197\u6708\u591a\u7528\u6c34
12/3.2=3.75\u5428
\u6545\u4e24\u4e2a\u6708\u5171\u7528\u6c34
36+36+3.75=75.75\u5428
\uff081\uff093.28\uff1b\uff082\uff09 \uff1b\uff083\uff0940. \u8bd5\u9898\u5206\u6790\uff1a\uff081\uff09\u7531\u524d20\u5428\u6c34\u7684\u8d39\u7528+\u8d85\u8fc720\u5428\u7684\u6c34\u8d39\u5efa\u7acb\u65b9\u7a0b\u6c42\u51fa\u5176\u89e3\u5373\u53ef\uff1b\uff082\uff09\u6839\u636e\u5206\u6bb5\u51fd\u6570\u6c42\u89e3\u7684\u65b9\u6cd5\u5f530\u2264x\u226420\u65f6\uff0c\u5f5320\uff1cx\u226430\u65f6\uff0c\u5f53x\uff1e30\u65f6\u5206\u522b\u7531\u603b\u8d39\u7528=\u5355\u4ef7\u00d7\u6570\u91cf\u5c31\u53ef\u4ee5\u6c42\u51fa\u7ed3\u8bba\uff1b\uff083\uff09\u5148\u6c42\u51fa\u524d30\u5428\u6c34\u8d39\uff0c\u518d\u6c42\u51fa\u7528\u4e8e\u7f34\u6c34\u8d39\u7684\u8d39\u7528\uff0c\u786e\u5b9a\u7532\u7528\u6c34\u91cf\u7684\u8303\u56f4\uff0c\u518d\u5efa\u7acb\u4e0d\u7b49\u5f0f\u6c42\u51fa\u5176\u89e3\u5373\u53ef\uff0e\uff081)\u7531\u9898\u610f\u5f97\uff0c20\u00d72.45\uff0b5 =65.4\u89e3\u4e4b\u5f97\uff0c =3.28 \uff082\uff09\u7531\u9898\u610f\u5f97\u5f530\u2264 \u226420\u65f6\uff0c \uff1b\u5f5320\uff1c \u226430\u65f6\uff0c \uff1b\u5f53 \uff1e30\u65f6\uff0c = \u5373 \uff083\uff096540\u00d72%=130.8 \u223520\u00d72.45=49\uff1b49\uff0b10\u00d73.28=81.8\u800c49\ufe6481.8\ufe64130.8 \u2234\u5c45\u6c11\u7532\u5bb66\u6708\u4efd\u7528\u6c34\u8d85\u8fc730\u5428\uff0c\u8bbe\u4ed6\u5bb66\u6708\u7528\u6c34 \u5428\uff0c\u5f97\uff0c \uff0d65.2\u2264130.8 \u89e3\u5f97\uff0c \u226440\u7b54\uff1a\u5c45\u6c11\u7532\u5bb6\u8ba1\u52126\u6708\u4efd\u6700\u591a\u7528\u6c3440\u5428 \uff0e
解：（1）16吨的水费为10*2.20+（16-10）*2.80=38.8元
（2）该户居民5月份用水超过18吨的部分为x吨
10*2.20+（18-10）*2.80+3.20x=57.2
x=4
所以5月份的总用水量为10+4=22吨
（3）6月份用水x吨
∵6 7月份总用水36吨，且7月份用水多余6月份，则6月份用水小于18吨
10*2.2+8*2.8+（36-x-18)*3.2-[10*2.2+(x-10)*2.8]=12
x=16
6月份用水16吨 7月份用水20吨
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