In order to encourage water saving, a city has made the following regulations on the charging standard of tap water: the part of water consumption no more than 10 tons per month is charged as 0.45 yuan / ton, while the part of water consumption no more than 20 tons is charged as 0.8 yuan / ton; the part of water consumption more than 20 tons is charged as 1.5 yuan / ton; in a month, a household pays 7.10 yuan more than B household, and B household pays 3.75 yuan more than C household, How much does the third household pay for water in that month? (tap water is charged according to the whole ton) The teacher seems to say that we should use functions

Let C use XT (0 ≤ x ≤ 10) and B use (10 + y) t (0 < y ≤ 10)
Then 0.45X + 3.75 = 0.8y + 0.45 × 10,
That is 9x-16y = 15
∵ 3 can divide 9 and 15, but not 16,
3 divising y
Y = 3 or 6 or 9
Only y = 3 is consistent with the meaning of the question, then x = 7
Similarly, if the water consumption of household a is (20 + Z) t, there will be
0.8y+0.45×10+7.10=1.50z+0.45×•0+0.8×10,
The solution is Z = 1
Therefore, a household pays 14 yuan, B household pays 6.9 yuan, C household pays 3.15 yuan. Comments: in this question, we should pay special attention to the subsection of charges, correctly analyze the value range of each household's water use, and then analyze and solve it according to the series equation of equal quantity and the integer number of water

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