Answer:

Step-by-step explanation:
There aren't any factors that cancel (except 3x). The best you can do is multiply it out.

Answer:

Step-by-step explanation:
The terms of this sum make the arithmetic sequence.
The fomula of a sum of <em>n</em> terms of an arithmetic sequence:
![S_n=\dfrac{[2a_1+(n-1)d]\cdot n}{2}](https://tex.z-dn.net/?f=S_n%3D%5Cdfrac%7B%5B2a_1%2B%28n-1%29d%5D%5Ccdot%20n%7D%7B2%7D)
We have

Substitute:
![S_{50}=\dfrac{[2\cdot2+(50-1)\cdot15]\cdot50}{2}=(4+49\cdot15)\cdot25=(4+735)\cdot25\\\\=739\cdot25=18,475](https://tex.z-dn.net/?f=S_%7B50%7D%3D%5Cdfrac%7B%5B2%5Ccdot2%2B%2850-1%29%5Ccdot15%5D%5Ccdot50%7D%7B2%7D%3D%284%2B49%5Ccdot15%29%5Ccdot25%3D%284%2B735%29%5Ccdot25%5C%5C%5C%5C%3D739%5Ccdot25%3D18%2C475)
Answer:
8978 grams
Step-by-step explanation:
The equation to find the half-life is:

N(t) = amount after the time <em>t</em>
= initial amount of substance
t = time
It is known that after a half-life there will be twice less of a substance than what it intially was. So, we can get a simplified equation that looks like this, in terms of half-lives.
or more simply 
= time of the half-life
We know that
= 35,912, t = 14,680, and
=7,340
Plug these into the equation:

Using a calculator we get:
N(t) = 8978
Therefore, after 14,680 years 8,978 grams of thorium will be left.
Hope this helps!! Ask questions if you need!!