Physics
posted by Judy .
A certian radioactive isotope has a halflife of 1 hour. If you start with 1 gram of the material at noon, how much of the original isotope will the sample contain at 3 pm? At 6 pm? At 10 pm?

A halflife is how long it takes for a radioactive isotope to decay by half.
At 2 PM, you will have .5 grams of the material.
Each hour thereafter, divide the material by half to see how much remains. 
A better way is with the exponential function on your calculator.
Amountremaining= Originalamount* e^(.692t/halflife)