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.