This is a simple proportion
1100 : 13 = 41000 : x
For every 1100 discs, 13 are defective, meaning that there will be an X number for each 41000
13 * 41000 = 1100 * x
13 * 410 = 11 * x
5330 = 11 * x
x = 5330/11
x = 484.5
That means that for every 41000, approximately 485 discs will break down.
