Posted by **Anonymous** on Monday, January 19, 2009 at 3:47pm.

5 e^-(t/5^2) = 1.5

e^-(t/125) = .3

e^(t/125) = 1/.3 = 3.3333

t/125 = ln 3.3333

t = 150.5

can some one please explain why it's 1/.3 and where the one comes from and where the negative sign goes.

Steps 2 to 3 is what i'm talking about

- math exponential -
**Reiny**, Monday, January 19, 2009 at 4:16pm
first of all, from line 1 to line 2 , 5^2 = 25 not 125.

So I don't know where the typo is, since the 125 is carried all the way from there.

from line 2 to line 3, the negative exponent rule was used, i.e.

if a^-n = p/q then

a^+n = q/p

illustrating with an example

2^-3 = 1/8

2^+3 = 8/1 or 8

if you first line was styped correctly then your solution would be

t/25 = ln 3.33333..

t = 83.3333.. or 83 1/3

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