Interest is the amount of money added on an amount invested. He have doubled her investment after 18 years
Compound interest
The formula for calculating the compound interest is expressed as
A = P(1+r)^t
Given the following parameters
P = $500
r = 4%= 0.04
A= $1000 (doubled)
Substitute
1000 = 500(1+0.04)^t
2 = 1.04^t
t = ln2/ln1.04
t= 17.67 = 18years
Hence he have doubled her investment after 18 years
Learn more on compound interest here: https://brainly.com/question/24924853
#SPJ1
