Question

$100,000 for 20 years compounded at 4 percent annually results in a rate per period of:

Answer 1

The Compound Interest Equation

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

where
P = future value
C = initial deposit
r = interest rate (expressed as a fraction: eg. 0.06)
n = # of times per year interest in compounded
t = number of years invested

When compounded annually, the equation can be simplified to:

P = C (1 + r)^t

P = 100000(1.04)^20
P = 219112.31

Not really sure what you mean by rate per period.