What is the half life of a substance if it decays by 75% in two weeks?

Answer 1

since it decays by 75% in two weeks, it has reduced to 1/4.

So, it reduces to 1/2 in 1 week.

half-life is one week.

Or, setting up aquation where t = no. of weeks,

A = Ao (1/4)^(t/2)

when is it at 1/2 Ao?

1/2 = (1/4)^(t/2)

square both sides:

1/4 = (1/4)^t

t = 1