40×(x+0.03)+60×(x-0.25)=42.73,
Solve this equation and get x=0.5635.
When x=0.5635,
x+0.03=0.5953,x-0.25 = 0.3 153; .
Answer: The electricity consumption of Xiaoming's home this month is 0.5953 yuan per kwh in the flat section and 0.3 153 yuan in the valley section.
(2)100× 0.5653-42.73 =13.8 (yuan)
Answer: If the time-of-use electricity price is not used for settlement, Xiaoming's family will pay more in May 13.8 yuan.