Help on Exponential Growth/Decay Question
Hi guys, I am doing A-levels and I came across two question I need help with.
We are told the exponential equation is P= ab^t
a= initial value
b=constant indicating how fast the quantity is growing
I know all but one value for the equation P= ab^-t, which is a. How Do I know the initial value of this substance?
A radioactive substance decays at rate of 12% per hour
a)Find after how many hours half of the radioactive material will be left.
b) How many hours did it have twice the current amount of radioactive material?
I have no idea how to do this one.
A dangerous radioactive substance has a half life of 90 years. It will be deemed safe when its activity is down to 0.005 of it's initial value. How long before it's deemed safe?
Thanks in advance.