If half of a radioactive isotope decays in one hour, how much of the original isotope will remain after three hours?

1/8

Explanation:

Use logic,

every one hour, half of a radioactive remains

for the first hour, half remains

for the second hour, half of half remains or quarter remains

for the third hour, 1/2 of 1/2 of 1/2 or 1/8 remains

or use this equation

where

n = amount after f time

r = amount of the original isotope

f = time

t = half-life