Answer:
15
Step-by-step explanation:
Ending Amount = Beginning Amount * e^k*t
5 grams = 100 grams * e^-.00043 * years
We have to solve the equation for "years"
(You can find the formula here: http://www.1728.org/halflif2.htm
or you can just read the next line
time = natural log (bgng amt / endg amt) / k
time = natural log (100 / 5) / .00043
time = natural log (20) / .00043
time = 2.9957322736 / .00043
time =
<span>
<span>
<span>
6,967</span></span></span><span> years
</span>
We should double-check this.
First, we need the half-life
k = ln(.5) / half-life
half-life = <span>-.693147 / -.00043
half-life = 1,612 years
Now let's see how many half-lives that is:
</span><span>6,967 / 1,612 years = 4.2 half-lives
So basically, after 4 half-lives the mass should go from
100
50 1 half life
25</span><span><span> 2 half lives</span>
12.5 </span><span>3 half lives
</span> 6.25 <span>4 half lives</span>
6.25 is very close to 5 grams so we can assume we have calculated correctly.
When you are subtracting over zeroes, you may need to carry over. This being said, you may need to take some from a previous number and put it into a zero, and continue carrying over until you can do what you needed to do. If you don't know the place value of the zero in mind, you will not end up completing this correctly.
Lilly has 74 and 13 inches of wood. How much wood does Lilly have in total?