ElectricPavlov

Thanx Guest 1.....I know I have seen you here before

There are people here that have formulas that far exceed my engineering economics from 30 years ago.....but I will try

FV=10,000

i= unknown  (ANNUAL interest rate)

PV=Present value (IF you ever learn ANYthing in life...learn the TIME-VALUE of money)=9770

FV = PV (1+i)^n     FV=10,000   PV=9770   i=?  n=1.5  (18 months is 1.5 years)

Plug and play

10,000 = 9770 (1 +i)^1.5

10,000/9770 = (1+i)^1.5

1.02354 =(1+i)^1.5              Take the LOG of both sides

.01010543 = 1.5 (log(1+i)    divide both sides by 1.5

.00673695 = log (1+i)          Both sides to power of 10

1.015633 = 1+i                    Subtract 1 from both sides

i=.015633=1.5633 %

I know I took the long route to get here......sometimes it's safer...haha

Ryo...THAT was cool !   Thanx for bein' here !  I learned something from your answer ...good.

Way cool, Melody...Thanx!  Power on Down Under.

OK...you are given most everything

T=40(given)= 20 + 80e^(-.06t)     I had to assume the '-.0.6t' was an exponent for the 'e' fxn

40= 20 + 80e^(-.06t)    Subtract 20 from each side

20 = 80 e^(-.06t)          Divide both sides by 80

.25 = e^(-.06t)             Take natural log (ln) of both sides

ln(.25) = -.06t       Simplify

-1.39629 = -.06t     dividey both sides by   -.06 

t=23.10 minutes      

Yah?

OK......got your ORIGINAL funcion.......when you differentiate constants go away.... when you INTEGRATE constants get added...are you differnetiatin w respect to x or y?

dx  or dy ?

Thanx!   It is always good to have + and - feedback .....that is how I RE-learn all of that 'stuff' from so long ago....

    G'Day ! (P.S.....Why not get an account?)

Some calculators will switch to EXPONENTIAL display...or SCIENTIFIC notation.... you lose some ACCURACY, but at such LARGE numbers it is usually insignificant.......YMMV

Thanx for your answer! It always helps ME to have a financial person on this site !

Really??? 'Time' magazine????  What a liberal piece of junk that is....Google is too!   C'mon ! What kind of brainwashing are you subliminally  being subjected to?????   THIS is a horribly biased question I will NOT answer.