Interest is the amount of money added on an amount invested. He have doubled her investment after 18 years
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
