Ive got a formula, that i cant solve: N (t)= 17,5 * a^t, where t is years, and that is 30,17 years, but i need to find a, how do i do that

The question. A certain radioactive substance has a half-life of 30,17 years. in the model you can calculate the remaining substance, as a function of time: N (t) = 17.5*a^t, where N (t) is remaining substance (measured in grams) and "t" is time (measured in years)...

When t=0

N(0)=17.5*a^0 = 17.5  So the original amount of substance is 17.5 grams.

The half life is the amount of time it takes for the original to decrease by half so N(30.17)=17.5/2=8.75grams

$$8.75=17.5*a^{30.17}$$

Divide both sides by 17.5 and you get

$$0.5=a^{30.17}$$

Raise both sides to the power of (1/30.17) and you will have the value of a    

$$N(30.17)=17.5*a^{30.17}$$

you have got 2 unknowns here. N(t) and a

You need to know what N(30.17 ) is before you can find a.

"N" is the amount of mass left after certain years, measured in grams

Yes I understand that but I need to know how much is left after 30.17 years in order to find a.

(or after any specific number of years for that matter)

It is not going to be the amount left either - the amount is growing all the time.

Perhaps you have an entire question that you can type in?

maybe i need to change the formular so it will say a=.. or something?

don't you have the original question in front of you?

Do you want to make a the subject?

The 30.17 years has no relevance unless you are given the N when t=30.17

The question. A certain radioactive substance has a half-life of 30,17 years. in the model you can calculate the remaining substance, as a function of time: N (t) = 17.5*a^t, where N (t) is remaining substance (measured in grams) and "t" is time (measured in years)...

Find "a" for the substance ??

Thank you soooo much Melody, can you please explain the last part, finding "a2 didnt get it :/

I'm lost, which bit didn't you understand?