Kelli's mom takes a 520 mg does of aspirin. Each hour, the amount of aspirin in a person's body system decreases by about 22%. After at least how many hours will the amount of aspirin in her body be less than 80 mg?

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 :)

a. is correct

addition

step-by-step explanation: