(1)由题意,得 100a=60 150a+b(200?150)=122.5 ,解得: a=0.6 b=0.65 .(2)设居民月用电为x度,由题意,得150×0.6+0.65(x-150)≤0.62x,解得:x≤250.答:月用电不超过250度时,其当月的平均电价每度不超过0.62元.故答案为:0.6,0.65.