Which expression is equal to 1/8000 written in scientific notation?
a. 8.0 x 10^3
b. 1.25 x 10^-10
c. 125 x 10^-5
d. 1.25 x 10^4

The answer is 1.25 · 10⁻⁴.

1/8000 = 0.000125 = 1.25 · 0.0001 = 1.25 · 10⁻⁴

Negative sign in superscript (10⁻⁴) is because it is decimal number 0.0001. If it was 10000 it would be positive sign: 10⁴

1/8000 = 1/8 x 1/1000 = 0.125 x 10^-3 = 1.25 x 10^-1 x 10^-3 = 1.25 x 10^(-1 + (-3)) = 1.25 x 10^(-1 - 3) = 1.25 x 10^-4