Answer:
we can write an equation wich describes the amount of aspirin in her system in respect to the hours (x)
a(x) = 520 * 0.78^x
78% is what's left on respect to one hour before and the "to the power of x" part describes how often we multiply/how many hours have passed
actually, if you haven't learned a better method yet, you could just grab your calculator, and type in 520 * 0,78
calculate it
then repeat multiplying the last answer till you go just below 80. the number of steps is the number of full hours passed.
this would take 8 steps
do you need a more sophisticated method to nail it down to the minute?
got no clue how far you are with the whole topic yet.
anyways, hope this helps you :)
