Question

PLEASE PLEASE PLEASE HELP ME WITH THIS WORD PROBLEM! IDK WHAT TO DO AT ALL!













The number of milligrams of a drug that remains in a patient's system after t hours is given by the function A(t) = Iert. Juan was given 500 milligrams of medicine which leaves his bloodstream at a rate of 20%. How much of the medicine remains in his system after 6 hours?
150.60 mg
133.90 mg
111.58 mg
99.20 mg

Answer 1

you can do this by simply subtracting 20 percent each time, it's similar to half-lifes (if you've ever done that)

hour 0:
200*0.2=40
hour 1:
160*0.2=32
hour 2:
160-32=128

etc

Answer 2

sorry change the 200 to 500

Answer 3

hour 0: 500

hour 1:
500*0.2=100 -> 500-100=400 left

hour 2:
400*0.2=80 -> 400-80=320 left

hour 3:
320*0.2=64 -> 320-64= 256 left

Answer 4

I am still lost..

Answer 5

It might be easier if you think of this in terms of what is left, rather than what is leaving.

If 20% leaves each hour, then after each hour passes, you have 100%-20% = 80% of the previous amount remaining. 80% = 80/100 = 0.8

At hour 0, you have 500
At hour 1 (1 hour elapsed), you have 500*0.8 = 400
At hour 2 (2 hours elapsed) you have 400*0.8 = 320
At hour 3 (3 hours elapsed) you have 320*0.8 = 256
and so on. Notice that you can also write this progression as

500 = 500
500*0.8 = 400
500*0.8*0.8 = 320
500*0.8*0.8*0.8 = 256

etc.
which is what the formula you were given does.

Answer 6

Are you familiar with compound interest? It's the same underlying concept.

Answer 7

not really..

Answer 8

is it gonna be b?

Answer 9

Get out your calculator. multiply 0.8*0.8*0.8*0.8*0.8*0.8*500. That's the amount left. Someone needs to calculate it to get the answer, it might as well be you :-)

Answer 10

I did the closest I got was to B

Answer 11

That must be it then!

Answer 12

its 121.072. kay thank ya!

Answer 13

131.072, actually