The bike repairs cost $20 because 80 x .25 = <<80*.25=20>>20
Call the amount he earns e. We know that e - 20 = 1/5e
Therefore 5e - 100 = e
Therefore, 4e = 100
Therefore, e = <<25=25>>25
Therefore, he sold 20 apples because 25 / 1.25 = <<25/1.25=20>>20
#### 20