Melody

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    

Hi BlindxD

I don't think that I am understanding this question properly.

24% did not answer the question at all

The number who answered it correctly is 1.5 times this which is 36% of the total students.

That makes a total of 60% the rest DID attempt the question but got it wrong.

That means that 40% of all the students is 10 students.

Now if 40% of All = 10 then

All=10*100/40 = 25 student

I thought that there was a problem but it was only in my imagination.  This is fine. 

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

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

Do you want to make a the subject?

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?

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

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

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

Beats me, did you look under your bed?

"PLZ ANSWER NOW" does not sound very polite!

If you have a cube with a volume of  343/1000cubic feet then each side will be     $$\frac{\sqrt[3]{343}}{\sqrt[3]{1000}} \;feet$$

You can do the calculation.

How to multiply what?

Hi Rosala,

The lowest common multiple of 2 and 5 is 10.  So I think the cube would have to have side length 10cm

If you let the front of the little rectangular prism (you call that a cuboid) be 2cm by 5cm

2*5=10 and 5*2=10 so there will be 5*2=10 0f these making up the front of the cube

The little boxes go back 5cm so you will need to double this to get 10 cm.

So the answer must be 5*2*2=20 little cuboids.

I'll see if I can draw it.