This can be solved using the formula
F = P ( 1+i ) ^n
Where F is the future worth
P is the principal amount
i is the interest rate
n is the number of years
at 5.84 per 1000 = 0.00584
F = 50000(1+0.00584)^20
F = 5617.56
At 15.66 per 1000 = 0.01566
F = 50000(1+0.01566)^20
F = 6822.40
So he will pay less = 6822.40 - 5617.56 = $1237.84
