Situation:
a 25 gram sample of a substance that’s used for drug research has a K-value of 0.1205.
N=N0e^-kt
N0(zero)= initial mass(at time t=0)
N= mass at time t
K= a positive constant that depends on the substance itself and on the units used to measure time
t= time, in days
Find the substances half-life, in days. Round your answer to the nearest tenths????

Question

Situation: 
a 25 gram sample of a substance that’s used for drug research has a K-value of 0.1205.
                                                                    N=N0e^-kt
N0(zero)= initial mass(at time t=0)
N= mass at time t
K= a positive constant that depends on the substance itself and on the units used to measure time
t= time, in days 
 Find the substances half-life, in days. Round your answer to the nearest tenths????

ribhu · Answer

i'll help u out with this.

ribhu · Answer

@brittany.hodges see, 
half life is that time when the concentration or mass becomes exactly half of which was taken initially.

anonymous · Answer

sorry but i still dont get it and i took notes like 30 times :/ @ribhu

ribhu · Answer

you have to be patient and with open mind, i bet i will make u understand.

ribhu · Answer

example if I take 1 gm of material and know that it will be left 0.5 gm at t=30 minutes so the half life would be 30 minutes. @brittany.hodges you have to stay with me here attentive.

anonymous · Answer

okay

anonymous · Answer

@ribhu

ribhu · Answer

so lets discuss ur problem.

anonymous · Answer

okay go ahead

ribhu · Answer

understand each and every variable like N, No etc.

anonymous · Answer

yes

anonymous · Answer

@ribhu

ribhu · Answer

since the k value has been given

ribhu · Answer

as i have already told u that half life would have the units same as time. so here in your question they are asking nothing but

ribhu · Answer

in what time the mass of sample decreases to 12.5 gm (since initial mass is 25gm)

ribhu · Answer

@brittany.hodges are u getting it? any doubt u have?

ribhu · Answer

is my method fine with u ? @brittany.hodges

ribhu · Answer

Now substituting the values
N=12.5 (at time t=t, here half life. )
No = 25
k= 0.1205
now its simple exponential equation where you need to calculate t.

ribhu · Answer

@brittany.hodges are u listening.

anonymous · Answer

yes im trying to rap my finger around it sorry

anonymous · Answer

@ribhu

ribhu · Answer

now did u get what i explained.

anonymous · Answer

yes im trying to plug it into the equation

ribhu · Answer

the method you must have got and concept of half life must have been cleared to u. @brittany.hodges

anonymous · Answer

i got t= 5.75225876

anonymous · Answer

@ribhu

ribhu · Answer

exactlyyyy

anonymous · Answer

yeah so after that i just plug it into the equaion and solve it?

ribhu · Answer

was i of help to you, probably better than ur notes. lol

anonymous · Answer

yeah thanks

ribhu · Answer

yeah thats it. or other wise one method is that $$No/2 = No e^-kt$$

ribhu · Answer

take ln both the sides and then the equation reduces to  $$\ln 2 / k$$

ribhu · Answer

this formula is always valid for these kind of question to calculate the half lives.

anonymous · Answer

okay thanks for all the help

ribhu · Answer

i hope i made it clear to u.

ribhu · Answer

@brittany.hodges

ribhu · Answer

are u sure u are clear with this? @brittany.hodges