exp. decay question. (2 Viewers)

[Zak Ambrose]

im having trouble with part 2. im almost sure im right though!

In an experiment, the amount of crystals, x grams, that dissolved in a solution after t minutes was given by:

x = 200(1 - e^-kt)

i) when t=3, x=50.... therefore k=0.09589


ii)at what rate were the crystals dissolving after 5 minutes. give your answer to the nearest gram.

i have redone ii and consistently get 12 grams. but the answer is 31.


am i just messing up or is 31 just not the correct answer.?

 

[oly1991]

u get 12 if u have:

19.178e(-0.09589 x 5)

u get 31 if u have:

19.178e(0.09589 x 5)

because k is actually -0.09589

 

[Zak Ambrose]

x= 200(1-(e^-kt))
dx/dt = 200k(e^-kt) where k= 0.09589......right?

when t = 5
dx/dt = 200(0.09589)e^(5x-0.09589).........right?
= 12........ right??