LW

Exponential Models

Compound Interest

A = P (1 + r / n) ^nt

Terms

Definitions

A

Expected amount after T years

P

Principle amount (initial)

R

interest rate (as decimal)

N

compounding period

T

time (in years)

Compounding Periods

n value

Yearly

n = 1

Semi-annually

n = 2

Tri-annually

n = 3

Quarterly

n = 4

Monthly

n = 12

Weekly

n = 52

Bi-weekly

n = 26

Daily

n = 365

Hourly

n = 8760

Continuously compounding

A = P * e^rt

Exponential Growth

A = P (1 + r)^t

Exponential Decay

A = P (1 - r)^t

Common Logs

Log (10) x = y

means 10 & y = 10

10^x and Log (x) are inverses, so:

Log (10^x) = x

10^(Log(x)) = x

Properties

Log (a) + Log (b) = Log (ab)

Log (a) - Log (b) = Log (a / b)

Log (a)^t = t * Log (a)

Log (10)^x = x

Natural Logs

Ln (x) = y means e^y = x

Ln (e^x) = x

e (ln(x)) = x

Properties

Ln a + Ln b = Ln (a*b)

Ln a - Ln b.= Ln (a / b)

Ln a&t = t * Ln a

Ln (e^x) = x

e ^ (Ln x) = x

Radioactive Decay

f(x) = P (0.5) ^ (x / h)

Term

Definition

P

Initial amount of substance

H

Half-life of substance

X

Time

f(x)

Substance left after X amount of time