85/100 in it's simplest form would be 0.85. However, if you want to keep it in fractional form, you can simplify it by finding the GCFs (Greatest Common Factors) of both. We can tell that both 85 and 100 are divisible by 5, because any number that ends in either a 5 or a 0 is (except 0).
85 / 5 = 17
100 / 5 = 25
85/100 simplifies to 17/25.
Hope that helped! =)