Iron-59 has a half-life of 44 days. a radioactive sample has an activity of 0.64 mbq. what is the activity of the sample after 88 days?

Radioactive decay is a pseudo-first order reaction. When you know the half-life of the material, you could use this equation.

A = A₀ (1/2) ^t/h

where

A is the final activity

A₀ is the initial activity

t is the time

h is the half-life

A = (0.64) (1/2) ^88/44 = 0.16 mbq