To write 8.4% as a fraction in simplest form, we write 8.4% as a fraction with a denominator of 100:
8.4% = 8.4/100
We can simplify this fraction by dividing both the numerator and denominator by their greatest common factor (GCF), which in this case is 4:
8.4/100 = 2.1/25
Therefore, 8.4% as a fraction in simplest form is 2.1/25.