We had in class following assignment which I had no idea how to get to the correct answer:

The carrion crow and the hooded crow are fertile together, but their reproductive success is reduced by 50%. In a certain region exist two populations of both species of roughly the same size. Thus, mixed couples occur in about 10% of all cases. What is the percentage of hybrids in the F1-generation?

(Translated from German.)

I thought it would be something like 5/95 = 5,3% but apparently the answer is 1%. Why?