Mr. Gardener wants to have the annual interest of $1000.00. If the annual interest rate is 5%, how much money should he invest?

Normally if mathematical fiance, interest rate should be accompanied by time period, in our case let's assume that Mr. Gardner wants annul interest of $1000, if the annual interest is 5%, the assumption is the money will have been invested for 1 year. 
Thus the total amount of money that can give us this interest rate given that it was invested for one year will be:
using simple interest:
I=(PRT)/100
interest I=$1000
principle, P=$x
rate, R=5%
time, T=1 year
hence:
1000=(x×5×1)/100
1000×100=5x
5x=100000
x=100000/5
x=20000
therefore, for him to make annual interest of $1000, he needs to invest $20000 through simple rate model.