Question

A certain radioactive substance is decaying so that at time t, measured in years, the amount of the substance, in grams, is given by the function f(t)=3e^(-3t). What is the rate of decay of the substance after half a year?

Answer 1

This is what I did. I found the derivative:
f'(t)=-9e^(-3t)
Then the half a year would be 1/2. I subbed that into t and got -2.00 as my answer. The answer is supposed to be -0.88 though

Answer 2

nope, that's all

Answer 3

ohhh

Answer 4

thanks anyway