The total number of light bulbs in the 20 lamps is 20*7 = <<20*7=140>>140
If 1/4 of the 20 lamps have burnt-out light bulbs, there are 1/4*20 = <<1/4*20=5>>5 lamps with burn out light bulbs
Since each of the 5 lamps has 2 burnt-out light bulbs, the number of burn out light bulbs is 2*5 = <<2*5=10>>10
The number of working light bulbs is 140 -10 = <<140-10=130>>130
#### 130