Answer:
the chance of a homozygous short-haired offspring if a heterozygous long-haired male mate with a short-haired is 50%
Explanation:
The best way to see this is to simply draw a punnett square. As you've said, let's call
S
the dominant trait (short hair) and
s
the recessive trait (long hair):
As shown in the image i uploaded:
As you can see, out of the 4 possible outcomes, 2 will result in short hair, and 2 in long. So, you'd have a chance of getting a short haired cat.