The function is:
B ( t ) = 4 * e^(0.8 t)
4 * e^(0.8 t) = 400
e^(0.8 t) = 400: 4
e^(0.8 t) = 100 / ln
ln e^(0.8 t) = ln 100 ( and since: ln e = 1 and ln e^x = x * ln e )
0.8 t = 4.6
t = 4.6 : 0.8 = 5.76 ≈ 6
Answer:
D ) 6 hours.
The exact form is:
-37/10
The decimal for is:
-3.7
The mixed number for is:
-3 7/10
Well, there are different ways to do this if you are really familiar with fractions, but "officially" :P
1) convert mixed numbers to improper fractions.
rule: a b/c = (ac+b)/c
2) make all fractions have a common denominator...
a/b+c/d
(a/b)(d/d)+(c/d)(b/b)
(ad/bd)+(cb/bd)
3)
The simplify your final answer with greatest common denominator or convert back to mixed number if needed...
