Blech, I think I'm still confused.
Set up all together, is it:
1/2 (4) = (4)(.981925)^10
Because I don't think that works. D:
you need to know what each term is. that way, you can translate from the word problem to the math equation and know what they are asking you for and what you are given.
is the amount left after a time has passed
is the initial amount. this is what we have when time is zero. nothing has started to decay yet
is the the amount of time that has passed.
now you found a in the first part, you are now given and you are asked for how much is left, namely . plug in what you know, and solve for what you don't