Set this up as
10 = 40 (1/2)t/28
and solve for t in years.
10/40 = (1/2)t/28
log(0.25) = (t/28) log(0.5)
t = 28 log(0.25) / log(0.5) years = 56 years
Test the answer:
56 years = 2(28 years) = 2 half-lives, so the remaining amount should be 1/2 of 1/2 of the initial amount, i.e. 1/4 of the initial amount, and 10 mg = 1/4 of 40 mg.
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It can be one of two things.
First, it can be due to global warming.
Second, it can be due to the rotation of the sun. When the sun rotates, it can change it latitude causing it to hit at different points onto different areas of the world.
The Biosphere is the answer that ur looking for
B: untied nations i do mj ethics